5925

RB1

OSRC|RB|p105-Rb|pRb|pp110;retinoblastoma 1;RB1;retinoblastoma 1

retinoblastoma suspectibility protein|retinoblastoma-associated protein

13q14.2

protein-coding

A presentation of intracranial tumor in bilateral and unilateral retinoblastoma with or without family history is termed as trilateral retinoblastoma (TRB). It always occurs either as a pineal tumor or supra/parasellar tumor, which differ in presentation and prognosis. We report here the first case of TRB with transmission of retinoblastoma gene (RB1) deletion from an unaffected mother (a carrier), presenting as concurrent intracranial neoplasm with bilateral retinoblastoma. The presence of RB1 mutation in both child and mother could be responsible for development of intracranial neoplasm which occurred simultaneously with bilateral RB in our patient. Our patient, who had a suprasellar mass, received radiation and intrathecal chemotherapy, and died 6 months after diagnosis. The occurrence of intracranial tumor in an asymptomatic stage can be avoided by routine computed tomography (CT) and magnetic resonance imaging (MRI) scan, and improved survival can be achieved by aggressive multimodality therapy.

Retinoblastoma, the most common intraocular malignancy ill childhood, has servedas a paradigm for the study of genetic mechanisms of oncogenesis. The retinoblastoma susceptibility gene RB1 was the first tumor suppressor gene to becloned, and genetic and molecular biologic studies of this tumor have greatly expanded the understanding of the mechanics of tumorigenesis. Human retinoblastoma has essentially no naturally occuring animal counterpart. The development of transgenic murine models of retinoblastoma have created an experimental tool for manipulation of a tumor gene system in vivo. These models have also enabled studies of new therapeutic modalities. This review outlines the development of the transgenic murine models of retinoblastoma, together with thegenetic mechanisms of retinoblastoma origin. Current therapeutic innovations developed by means of the transgenic models are described.

We present a case of multifocal osteosarcoma (MFOS) arising 11.5 years after successful treatment of bilateral retinoblastoma. The clinical, imaging and pathological findings at onset, after therapy, and during follow-up are described. Fluorescent in situ hybridization did not reveal a deletion of the RB-1 retinoblastoma gene, although the presence of an inactivating mutation invisible to this method cannot be ruled out. The MFOS may have been a second multifocal tumor associated with the original retinoblastoma or a post-irradiation sarcoma with extensive metastases.

We present a case of multifocal osteosarcoma (MFOS) arising 11.5 years after successful treatment of bilateral retinoblastoma. The clinical, imaging and pathological findings at onset, after therapy, and during follow-up are described. Fluorescent in situ hybridization did not reveal a deletion of the RB-1 retinoblastoma gene, although the presence of an inactivating mutation invisible to this method cannot be ruled out. The MFOS may have been a second multifocal tumor associated with the original retinoblastoma or a post-irradiation sarcoma with extensive metastases.

The organization of genomic DNA into chromatin aids in the regulation of gene expression by limiting the access of transcriptional binding domains. The SWI/SNF family of chromatin-remodeling complexes, which are conserved from yeast to humans, open the chromatin to facilitate the transcriptional machinery to accesstheir targets. The gene encoding the BAF47/hSNF5 subunit of the complex has beenfound mutated in both rhabdoid cell lines and in primary rhabdoid tumors. Since the pediatric tumors rhabdomyosarcoma (RMS) and Wilms' tumor (WT) share a similar genetic link with rhabdoid tumors, it was hypothesized that they may also show alterations of the BAF47 gene. Using primary tumors, the BAF47 protein was detected in ALL WT but less than 75% of the RMS tested. In cell lines, the BAF47protein was missing in ALL rhabdoid cell lines and one RMS cell line. Analysis of sample DNA displayed either a mutation or deletion of the BAF47 gene in ALL samples negative for the protein. Several other subunits of the human SWI/SNF complex, including BRG1 which is the subunit directly interacting with the Rb tumor suppressor gene, were detected in ALL tumor samples. Alteration of BAF47 may be a genetic marker associated with the poor prognosis seen in ALL rhabdoid tumors but only some RMS.

Brain tumors are among the most common forms of cancer in children and account for most cancer-related deaths in this age group. The incidence of brain tumors appears to be increasing in children, while therapeutic advances have been modest. Few genetic studies exist on pediatric brain tumors, in part because tissue from low-grade and brain stem tumors is not readily available, and also because individual centers have relatively few cases. Genetic changes in infiltrating astrocytomas involve genes in the p53 and RB pathways, and show alterations that are similar to infiltrating astrocytomas in adults. The PTC gene is mutated in a subgroup of medulloblastomas, and may lead to increased proliferation in granule cells that normally express this receptor. Further studies are needed to identify genetic alterations in pilocytic and low-grade astrocytomas, which account for 40% of brain tumors in children.

Retinoblastoma, a rare pediatric eye tumor, has served as an important model forthe heritable predisposition to cancer. The retinoblastoma protein, Rb, functions as a tumor suppressor by controlling progression through the cell cycle. Rb function is regulated primarily by its phosphorylation state, which is determined by the complex interaction of multiple kinases and their inhibitors that together form the 'Rb pathway'. This pathway has been found to be functionally inactivated in almost ALL types of cancer. Despite recent advances in our understanding of Rb function, the precise role of Rb loss in the development of retinoblastoma remains unclear. Recent work in genetically altered mice has suggested that an additional mutation in another gene is required for retinal tumor formation. An alternative model presented here is based on the noncell-autonomous functions ofRb contributing to tumorigenesis.

BACKGROUND: Deregulation of tumor suppressor gene function and abrogation of cell cycle control are common features of malignant neoplasms, but corresponding dataon Ewing sarcomas and primitive neuroectodermal tumors are relatively scarce. Westudied the expression of 4 tumor suppressor proteins in the Ewing family of tumors (EFTs). DESIGN: We examined a series of 20 pediatric EFTs for abnormal expression of p16(INK4a), p14(ARF), p21(WAF1), and pRB by immunohistochemical analysis of pretreatment, nondecalcified archival specimens. Clinical follow up was available in ALL cases (median, 21 months; range, 5-103 months). Five patients presented with metastatic disease, 8 had no evidence of disease at lastfollow up, and 12 had an adverse outcome (death or progressive tumor posttherapy). RESULTS: Twelve cases (60%) demonstrated abnormal expression of atleast one tumor suppressor protein. There were 11 cases (55%) with loss of p21(WAF1) expression, 4 (20%) with down-regulation of p16(INK4a), 2 (10%) with absence of pRB, and one case (5%) with loss of p14(ARF) expression. Loss of p16(INK4a) expression correlated with metastatic disease at presentation (P =.026), and showed a trend toward shortened survival (P =.20). The p21(WAF1), p14(ARF), and pRB status was not significantly correlated with either metastaticdisease at presentation or outcome. CONCLUSION: Abrogation of the G1 checkpoint was common in this series of EFTs, and down-regulation of p21(WAF1) and p16(INK4a) were the most frequent findings. Loss of p16(INK4a) expression may identify a subset of cases with a more aggressive phenotype.

Results of recent studies have led investigators to suggest that the retinoblastoma tumor-suppressor (rb) gene plays an underappreciated role in the genesis of brain tumors. Such tumors cause significant rates of mortality in children suffering from hereditary retinoblastoma. It has been assumed that the pineal gland, which is ontogenetically related to the retina, accounts for the intracranial origin of these trilateral neoplasms. To address this issue, the authors describe an unusual trilateral retinoblastoma variant. The authors provide a detailed clinicopathological correlation by describing the case of a child with bilateral retinoblastoma who died of a medulloblastoma. The intraocular and intracranial neoplasms were characterized by performing detailedimaging, histopathological, and postmortem studies. Karyotype analysis and fluorescence in situ hybridization were used to define the chromosomal defect carried by the patient and members of her family. An insertion of the q12.3q21.3segment of chromosome 13 into chromosome 18 at band q23 was identified in members of the patient's family. This translocation was unbalanced in the proband. The intraocular and cerebellar neoplasms were found to be separate primary neoplasms. Furthermore, the pineal gland was normal and the cerebellar neoplasm arose within the vermis as a medulloblastoma. Finally, the two neoplasms had different and characteristically identifiable cytolological and immunohistochemical profiles. The findings of the present study, taken together with those of recent molecularand transgenic studies, support the emerging concept that rb inactivation is notrestricted to central nervous system regions of photoreceptor lineage and that inactivation of this tumor suppressor pathway may be relevant to the determination of etiological factors leading to medulloblastoma in humans.

Results of recent studies have led investigators to suggest that the retinoblastoma tumor-suppressor (rb) gene plays an underappreciated role in the genesis of brain tumors. Such tumors cause significant rates of mortality in children suffering from hereditary retinoblastoma. It has been assumed that the pineal gland, which is ontogenetically related to the retina, accounts for the intracranial origin of these trilateral neoplasms. To address this issue, the authors describe an unusual trilateral retinoblastoma variant. The authors provide a detailed clinicopathological correlation by describing the case of a child with bilateral retinoblastoma who died of a medulloblastoma. The intraocular and intracranial neoplasms were characterized by performing detailedimaging, histopathological, and postmortem studies. Karyotype analysis and fluorescence in situ hybridization were used to define the chromosomal defect carried by the patient and members of her family. An insertion of the q12.3q21.3segment of chromosome 13 into chromosome 18 at band q23 was identified in members of the patient's family. This translocation was unbalanced in the proband. The intraocular and cerebellar neoplasms were found to be separate primary neoplasms. Furthermore, the pineal gland was normal and the cerebellar neoplasm arose within the vermis as a medulloblastoma. Finally, the two neoplasms had different and characteristically identifiable cytolological and immunohistochemical profiles. The findings of the present study, taken together with those of recent molecularand transgenic studies, support the emerging concept that rb inactivation is notrestricted to central nervous system regions of photoreceptor lineage and that inactivation of this tumor suppressor pathway may be relevant to the determination of etiological factors leading to medulloblastoma in humans.

Rhabdomyosarcoma (RMS) is a family of soft tissue tumors that are associated with the skeletal muscle lineage and generally occur in the pediatric population. Based on histopathologic features, two subtypes, embryonal (ERMS) and alveolar (ARMS), were identified and associated with distinct clinical characteristics and genetic alterations. ARMS is associated with 2;13 or 1;13 chromosomal translocations, which generate PAX3-FKHR and PAX7-FKHR fusion products, respectively. These translocations result in altered expression, function, and subcellular localization of the fusion products relative to the wild-type proteins, and ultimately contribute to oncogenic behavior by modifying growth, differentiation, and apoptosis pathways. In contrast to the specific translocations found in ARMS, most ERMS cases have allelic loss at chromosome 11p15.5. Chromosome fragment transfer studies demonstrated that this region represses tumor cell growth, suggesting the presence of tumor suppressor gene(s)in this region. In both ERMS and ARMS, there is evidence of collaborating alterations that affect common targets, such as the p53 and RB pathways. One mechanism for perturbing these pathways involves amplification of genes such as MDM2 and CDK4; these amplification events occur frequently in ARMS but only rarely in ERMS. Therefore, despite similarities in the downstream targets of these genetic alterations, the striking cytogenetic and molecular differences between ARMS and ERMS indicate distinct molecular etiologies in these two subtypes.

OBJECTS: Atypical teratoid/rhabdoid tumors (AT/RT) are aggressive neoplasms thatafflict infants and young children. The objective of this retrospective study was to determine the association between DNA content (DNA ploidy, cell cycle analysis), tumor suppressor gene (p53, pRb, p16, and MMAC/PTEN) expression and the biologic aggressiveness of these tumors. METHODS: Eight tumors from 7 patients (1 girl, 6 boys; median age 4+/-6.7 months) were studied. Two patients had DNA aneuploidy and 5 patients manifested diploid DNA content at diagnosis. The proliferative index of the tumors ranged from 10% to 28% (median, 12+/-6.4%). The single tumor with a low proliferative index (i.e., <10%) was aneuploid. Immunohistochemical evaluation of p53, pRb, p16, and MMAC/PTEN expression patterns showed that most of the tumors contained more cells with abnormal pRb and p16 expression than cells with abnormal p53 and MMAC/PTEN expression. expression of tumor suppressor genes, however, was inhomogeneous. CONCLUSION: Our findings led us to conclude that AT/RT of childhood is characterized by a high proliferative index and DNA aneuploidy. The high expression of abnormal pRb and p16 and the low expression of abnormal p53 and MMAC/PTEN indicate alteration of the G1-to-S phase step in the cell cycle, which could be an explanation for the aggressive nature of these tumors.

Retinoblastoma (RB) is a childhood tumor of the eye with an average incidence ofone case in every 15,000-20,000 live births and occurs in sporadic or hereditaryform. This cancer results from loss or inactivation of the RB1 gene located at 13q14.1. This gene encodes for a 110 Kd nuclear phosphoprotein (pRB) that plays a major role in cell proliferation control. Different types of mutations in the RB1 gene have been reported, but point mutations are the most common. There are no molecular studies on RB1 gene mutation in Mexican patients. In this study, 19 patients with bilateral or unilateral RB were analyzed. Genetic and cytogenetic studies were carried out. Detection of RB1 gene mutations was done using single-strand conformational polymorphism (SSCP). Five conformational polymorphisms were identified in different exons. In ALL cases, SSCP sequence showed new non-described mutations that produced a frameshift on the open reading frame. The identification of mutations in the RB1 gene contributes to basic knowledge of this neoplasia and permits the possibility to offer adequate genetic counseling to relatives at risk.

PURPOSE: To analyze the genetic and epigenetic alterations affecting the RB1, TP53, p16INK4, and p21WAF1 tumor suppressor genes, loss of heterozygosity (LOH) at 3q and 18q, and the clinical variables of a series of Spanish children with osteosarcoma. These genetic changes were tested for an association with prognosis. METHODS: Peripheral blood samples and clinical data were available from 76 patients with osteosarcoma. Paired tissue was available from 41 of them.The mutation and methylation status of p16INK4, p21WAF1, TP53, and RB1 was screened as well as LOH at 3q and 18q. RESULTS: Loss of heterozygosity affectingRB1 (37.2%), TP53 (42.3%), and 18q (30.8%) and TP53 mutation (39%) were frequently encountered. TP53 mutation was associated with diagnosis at a later age. RB1 alteration was associated with reduced survival and event-free survival. The clinical variables associated with poor prognosis were the presence of metastasis at diagnosis (P = 0.035) or during treatment (P = 0.016) and the chondroblastic histologic subtype (P = 0.007); the response to induction chemotherapy (<90% necrosis) also tended to be related to poor prognosis (P = 0.08). CONCLUSIONS: RB1, TP53, and possibly other tumor suppressor genes locatedat 18q and other localizations are involved in pediatric osteosarcoma carcinogenesis, together with other genetic alterations not fully understood to date. Based on these results, the presence of an altered RB1 gene should be regarded as a poor prognostic factor for pediatric osteosarcoma.

BACKGROUND: Several tumor suppressor genes such as p16INK4, TP53, RB1 y p21WAF1 are involved in cell cycle regulation in response to DNA damage and belong to the complex pathway that regulates cell proliferation and/or differentiation. We have investigated the presence of mutations in those genes and polymorphisms of Drug Metabolizing Enzymes that could be involved in the development of pediatric bonetumors or in their outcome. MATERIALS AND METHODS: By means of PCR-based techniques, we have analyzed the presence of variations in the coding sequence of p16INK4, TP53, RB1 y p21WAF1 and of the Drug Metabolizing Enzymes in a group of 82 osteosarcomas and 47 Ewing's sarcomas as well as in a control group of 115 healthy children. RESULTS: We detected mutations of the TP53 gene in about 25% of the samples analyzed, most frequently in association with tumors of poor prognosis or reduced survival. The p16INK4 gene was homozygously deleted in 18% of the osteosarcomas, also associated with poor prognosis and unfavourable histologic subtypes; RB1 was altered in 21% of the osteosarcomas. We did not detect relevant associations between polymorphisms of the Drug Metabolizing Enzymes or mutation of the p21WAF1 and development of pediatric bone tumors. CONCLUSIONS: Alteration of TP53, p16INK4 and p21WAF1 seems to be involved in thedevelopment of pediatric bone tumors and to be an unfavourable prognostic factorin this type of tumors.

RB1 is the gene responsible for retinoblastoma, the most common malignant intraocular tumor of infancy and early childhood. There are no reports about this gene in Ecuadorian populations, and only a few studies have been published in Latin America about this subject. There is a spectrum of more than 370 mutationsdescribed in the RB1 gene mutation database (http://www.d-lohmann.de/Rb/mutations.html), and alterations have been found in 25 of the 27 exons. During the exon-by-exon analysis of 31 tumor and blood samples from Ecuadorian patients, we found two new mutations and three novel polymorphisms. One of the polymorphisms is located in intron 26 where no alterations of the gene have been described previously. The polymorphisms were found in ALL of the patients' tumor samples, but not in normal population, suggesting there might be a relationship between these polymorphisms and the development of retinoblastoma in the Ecuadorian population.

mutational inactivation of the retinoblastoma gene (RB) is an invariant feature of the childhood eye cancer retinoblastoma and of tumor cells derived therefrom.In a previous study, retrovirus-mediated transfer of wild-type RB into cultured retinoblastoma cells resulted in a marked enlargement and reduced growth rate ofthese cells, as well as loss of their tumorigenic properties in nude mice. It was therefore difficult to separate the proposed growth-suppressing and tumor-suppressing activities of RB protein. Here, we show that clones of RB-reconstituted retinoblastoma cells can be isolated that stably express apparently normal RB protein for at least 20 months of continuous culture. Theseclones were indistinguishable from nonreconstituted cells by multiple parametersincluding morphology, growth rate, and cell cycle distribution. Despite similar phenotypes in culture, clones with stable RB expression were uniformly nontumorigenic in nude mice, whereas those that lost such expression regained their tumorigenic properties. These results indicate that the tumorigenicity of these cells is entirely determined by the presence or absence of exogenous RB protein expression and that suppression of tumorigenicity is distinct from inhibition of cellular growth in culture.

One major factor hindering progress of pediatric cancers of the nervous system has been the lack of satisfactory model systems for testing novel therapies. A mouse strain, mutant for the Rb1 gene was generated 12 years ago in the hope of producing a model in which to study retinoblastoma. Surprisingly, the Rb(+/-) mice never developed retinoblastoma. Now, Zhang, Schweers and Dyer produce triply deficient Rb, p107 and p53 mutant retinal progenitor cells. ALL such mice develop intraocular retinoblastoma with invasion of the tumor into the anterior chamber of the eye. This dramatic finding represents the first description of a heritable mouse model of retinoblastoma, which has eluded investigators for the last 12 years. Such models provide an unprecedented opportunity to advance knowledge of tumorigenesis and to develop non-toxic intervention strategies which eradicate disease.

pediatric neurogenic tumors include primitive neuroectodermal tumors (PNETs), especially medulloblastoma; ependymomas and choroid plexus papillomas; astrocytomas; retinoblastoma; and sympathetic neuroblastoma. Meningiomas and nerve sheath tumors, although uncommon in childhood, are also significant because they can result from exposures of children to ionizing radiation. Specific chromosomal loci and specific genes are related to each of these tumor types. Virtually ALL these genes appear to act as tumor suppressor genes, which are inactivated in tumor cells by mutations or by chromosomal loss. In genetically engineered mice, some genes that are clearly associated with specific human tumors (e.g., RB1 in retinoblastoma and NF2 in meningiomas and schwannomas) haveno such effect. Other genetic constructs in mice involving the genes p53, ptc1, and Nf1 have produced tumors remarkably similar to some of the human pediatric neoplasms. Some of these tumors become clinically apparent after only a few weeks, while the mice are still juveniles, especially when two or more tumor suppressor genes are inactivated in the same genetic construct. Conversely, at least one genetic pathway in rodents involving point mutation in the coding region of a transforming gene (neu in malignant schwannomas) does not appear to operate in any human tumors. The nervous system is markedly susceptible to experimental carcinogenesis during early life in rodents, dogs, primates, and other nonhuman species, and there is no obvious reason why this generalization should not also apply to humans. However, except for therapeutic ionizing radiation, no physical, chemical, or biological cause of human pediatric nervoussystem tumors is known. The failure of experimental transplacental carcinogenesis to mirror human pediatric experience more closely may reflect the need for multiple mutational events in target cells, and for experimental carcinogens that are capable of causing the full spectrum of mutations that occur in cancer-related genes in pediatric neurogenic tumors.

Although much less prevalent than its nonmelanoma skin cancer counterparts, cutaneous malignant melanoma (CMM) is the most lethal human skin cancer. Epidemiological and biological studies have established a strong link between lifetime exposure to ultraviolet (UV) light, particularly sunburn in childhood, and the development of melanoma. However, the specific molecular targets of thisenvironmental carcinogen are not known. Data obtained from genetic and molecularstudies over the last few years have identified the INK4a/ARF locus as the "gatekeeper" melanoma suppressor, encoding two tumour suppressor proteins in human, p16 $^{ ext{INK4a}}$ and p $14^{ ext{ARF}}$ . Recent developments in molecular biotechnology and research using laboratory animals have made a significant gene breakthrough identifying the components of the p16 $^{ ext{INK4a}}$ /Rb pathway as the principal and rate-limiting targets of UV radiation actions in melanoma formation. This review summarizes the current knowledge of the molecular mechanisms involved in melanoma development and its relationship to sunlight UV radiation.#FAU - Williams, Mandy

Aberrant expression of tumor suppressor genes WT 1, RB 1, p53, homozygous deletion of p16 gene and their relationship with expression of oncogenes BCR-ABL, TEL-AML 1, MLL-AF 4, E2A-PBX 1, SIL-TAL 1 were determined in bone marrow samplesof children with de novo B-lineage (n=170) and T-lineage (n=25) acute lymphoblastic leukemia (ALL). In contrast to expression of chimeric oncogenes alterations in p16, WT 1, RB 1 and p53 expression were T/B-lineage-unrestricted.Significant association between expression of MLL-AF 4 and WT 1, E2A-PBX 1 and p53; SIL-TAL 1 and homozygous deletion of p16 has been demonstrated.

pediatric glioblastoma multiforme (GBM) tumors, which have been established as 'de novo' neoplasms, are known to differ from their adult counterparts in terms of biology, genetics and ultimately survival of patients. In order to evaluate the utility of markers of tumor biology for refining prognostic assessment, we retrospectively analyzed 54 pediatric GBMs (age range 9 months to 15 years) occurring at different anatomical sites in the brain, operated at our institute between 1995 and 2001. The expression of p53, epidermal growth factor receptor (EGFR), bcl-2 and retinoblastoma proteins (pRb) was analyzed by immunohistochemistry and the results were compared with the clinical profile, MIB-1 labeling index (LI) and patient survival. p53 immunoreactivity was noted in 53.7% of cases, predominantly in thalamic (75%) and cerebral lobar (62.2%), followed by brainstem tumors (30%). It was absent in cerebellar tumors. p53-positive tumors had a higher MIB-1 LI, compared to p53-negative tumors (p=0.003). EGFR and bcl-2 overexpression was observed in 25.9% and 33.3% of cases, respectively, and loss of pRb expression was evident in only 7.4% of cases, indicating that loss of this gene function is not significantly involved in pediatric GBMs. p53 and bcl-2 expression were maximally noted in patients with poorer outcome. Our results indicate that p53 expression status is noted in a significant number of pediatric supratentorial neoplasms. p53 with bcl-2 overexpression is more often associated with ominous prognosis. Further molecular characterization would provide newer insights into the biology of these neoplasms and form a basis for future therapeutic decision making.#CI- Copyright (c) 2005 S. Karger AG, Basel.

Retinoblastomas are the most frequent intraocular tumors in childhood. Untreated, the tumor is almost always fatal. Using a multidisciplinary approach combining the efforts of ophthalmologists, radiation oncologists, pediatric oncologists and geneticists a survival rate of more than 95% can be achieved. Molecular genetic research on the origin of retinoblastomas has substantially helped in our understanding of the origin of malignant tumors in general, as well as to the key role of the Rb-1 gene as a tumor suppressor.

Retinoblastoma, an uncommon childhood cancer of the eye, sometimes occurs in families but is often sporadic. Cytological analysis suggested that the retinoblastoma gene resided on chromosome 13 band q14. Subsequent isolation of the RB gene from this locus allowed a more detailed analysis, showing that both copies of RB are mutated or lost in retinoblastoma, a finding that has been extended to a surprising number of other malignancies. In familial retinoblastoma, one copy of RB is mutant in the conceptus, consistent with the familial predisposition to the disease and indicating that a single wild type copy is sufficient for normal development. These studies provided the first goodevidence that loss of a gene function correlated with tumorigenesis and led to the concept of "tumour suppressor genes", which have an important negative influence on the regulation of cell growth. Examinations of the biological properties of the gene product are consistent with this proposed role in cell proliferation. Further insight into the potential molecular mechanisms concernedhas come from observations showing an association of some viral oncoproteins with the RB gene product. Thus, there is strong evidence that the RB protein has a key role in the integrated network of signals that control the cell cycle.

Genesis of the childhood ocular tumor retinoblastoma results from the mutationalinactivation of a single gene, RB, located on chromosome 13. Cultured cells or cell lines derived from retinoblastomas have been extensively studied for insight into mutational mechanisms of RB inactivation, functional properties of wild-type RB alleles, and pathways of retinal differentiation. Three such cell lines (Y79,RB355 and WERI-Rb27) were previously shown to have similar, heterozygous rearrangements of their RB genes, suggesting a common mutational mechanism affecting a specific region of the gene. This proposal was based on the premise that ALL three mutations occurred independently. By using molecular analyses of human genetic polymorphisms, we now show that these three cell lines are in factgenetically related, despite their different origins, morphologies, growth characteristics, and karyotypes. Interpretation of these and other published data suggest that both RB355 and WERI-Rb27 are probably sublines of Y79.

Retinoblastoma is a rare eye tumor of childhood that arises in the retina. It isthe most common intraocular malignancy of infancy and childhood; with an incidence of 1/15,000-20,000 live births. The two most frequent symptoms revealing retinoblastoma are leukocoria and strabismus. Iris rubeosis, hypopyon,hyphema, buphthalmia, orbital cellulites and exophthalmia may also be observed. Sixty per cent of retinoblastomas are unilateral and most of these forms are nothereditary (median age at diagnosis two years). Retinoblastoma is bilateral in 40% of cases (median age at diagnosis one year). ALL bilateral and multifocal unilateral forms are hereditary. Hereditary retinoblastoma constitutes a cancer predisposition syndrome: a subject constitutionally carrying an RB1 gene mutation has a greater than 90% risk of developing retinoblastoma but is also at increased risk of developing other types of cancers. Diagnosis is made by fundoscopy. Ultrasound, magnetic resonance imaging (MRI) and computed tomography (CT) scans may contribute to diagnosis. Management of patients with retinoblastoma must take into account the various aspects of the disease: the visual risk, the possibly hereditary nature of the disease, the life-threatening risk. Enucleation is still often necessary in unilateral disease; the decision for adjuvant treatment is taken according to the histological risk factors. Conservative treatment for at least one eye is possible in most of the bilateral cases. It includes laser alone or combined with chemotherapy, cryotherapy and brachytherapy. The indication forexternal beam radiotherapy should be restricted to large ocular tumors and diffuse vitreous seeding because of the risk of late effects, including secondary sarcoma. Vital prognosis, related to retinoblastoma alone, is now excellent in patients with unilateral or bilateral forms of retinoblastoma. Long term follow-up and early counseling regarding the risk of second primary tumors and transmission should be offered to retinoblastoma patients.

Retinoblastoma is the most common primary intraocular tumor in childhood. mutations in both the alleles of the RB1 gene represent the causative agent for the tumor to occur. It is becoming evident that, although these alterations represent key events in the genesis of retinoblastoma, they are not sufficient per se for the tumor to develop, and other additional genetic or epigenetic alterations must occur. A supportive role in the genesis of retinoblastoma has recently been proposed for the RB1-related gene RB2/p130. Additionally, several other genetic alterations involving different chromosomes have been described asrelevant in the tumorigenic process. In this review we will analyse current knowledge about the molecular mechanisms involved in retinoblastoma, paying particular attention to the mechanisms of inactivation of the biological function of the retinoblastoma family of proteins.

tumors of the nervous system most often occur in both children and adults as sporadic events with no family history of the disease, but they are also among the clinical manifestations of a significant number of familial cancer syndromes, including familial retinoblastoma, neurofibromatosis 1 and 2, tuberous sclerosis, and Cowden, Turcot, Li-Fraumeni and nevoid basal cell carcinoma (Gorlin) syndromes. ALL of these syndromes involve transmissible genetic risk resulting from loss of a functional allele, or inheritance of a structurally defective allele, of a specific gene. These genes include RB1, NF1, NF2, TSC1, TSC2, TP53,PTEN, APC, hMLH1, hPSM2, and PTCH, most of which function as tumor suppressor genes. The same genes are also observed in mutated and inactive forms, or are deleted, in tumor cells in sporadic cases of the same tumors. The nature of the mutational events that give rise to these inactivated alleles suggests a possible role of environmental mutagens in their causation. However, only external ionizing radiation at high doses is clearly established as an environmental cause of brain, nerve and meningeal tumors in humans. Transplacental carcinogenesis studies in rodents and other species emphasize the extraordinary susceptibility of the developing mammalian nervous system to carcinogenesis, but the inverse relationship of latency to dose suggests that low transplacental exposures to genotoxicants are more likely to result in brain tumors late in life, rather than in childhood. While not ALL neurogenic tumor-related genes in humans have similar effects in experimental rodents, genetically engineered mice (GEM) increasingly provide useful insights into the combined effects of multiple tumor suppressor genes and of gene-environment interactions in the genesis of brain tumors, especially pediatric brain tumors such as medulloblastoma.

Human retinoblastoma is a pediatric cancer initiated by RB gene mutations in thedeveloping retina. We have examined the origins and progression of retinoblastoma in mouse models of the disease. Retina-specific inactivation of Rb on a p130-/- genetic background led to bilateral retinoblastoma with rapid kinetics, whereas on a p107-/- background Rb mutation caused predominantly unilateral tumors that arose with delayed kinetics and incomplete penetrance. In both models, retinoblastomas arose from cells at the extreme periphery of the murine retina. Furthermore, late retinoblastomas progressed to invade the brain and metastasized to the cervical lymph nodes. Metastatic tumors lacking Rb and p130 exhibited chromosomal changes revealed by representational oligonucleotide microarray analysis including high-level amplification of the N-myc oncogene. N-myc was found amplified in three of 16 metastatic retinoblastomas lacking Rb and p130 aswell as in retinoblastomas lacking Rb and p107. N-myc amplification ranged from 6- to 400-fold and correlated with high N-myc-expression levels. These murine models closely resemble human retinoblastoma in their progression and secondary genetic changes, making them ideal tools for further dissection of steps to tumorigenesis and for testing novel therapies.

BACKGROUND: Retinoblastoma (RB) is a malignant tumor originating in the retinal cell precursors and can be presented as a unilateral or bilateral form in childhood (one or both eyes affected). Development of this tumor is caused by mutations in the RB1 gene on chromosome 13q14; the first mutation may occur in the germ line (hereditary RB) or in somatic cells (non-hereditary RB). The hereditary form of RB is transmitted with a high penetrance to offspring (90%). Because early diagnosis is necessary for implementing effective treatment and preserving vision, it is important to identify the mutations in the affected family. AIM: The aim of this study was to identify large and small RB1 germ-linemutations and to correlate them with the RB phenotype. METHODS: Constitutional RB1 gene gross deletions were studied in 40 patients with bilateral or unilateral familial RB by a segregation assay of four intragenic polymorphisms located in introns 1, 4, 17, and 20 of the RB1 gene, along with fluorescence in situ hibridization (FISH) analysis. Small mutations were ascertained in a subgroup often patients by heteroduplex/sequence analysis of RB1-exons. RESULTS: In the course of our study, we have found three large deletions, which probably represent whole gene deletions, and two small deletions of 1bp in length. One large deletion was found in a family with several members affected. This represents a rare case of familial RB, which is usually caused by small mutations. Phenotype analysis of the family revealed a low penetrance inheritance, with an 'affected eyes : number of mutation-carriers' ratio of approximately 1.0, whereas this ratio in families with small loss-of-function mutations is 1.5-2.0. CONCLUSIONS: Our results emphasize the usefulness of a combined methodology that includes segregation of polymorphisms, FISH, and heteroduplex/sequence analyses for detection of gross and small DNA rearrangements in familial and sporadic RB. Identification of mutations in sporadic cases is important for risk-assessment in patients' relatives. The degree of penetrance in the inheritance of RB not only depends on the occurrenceof the second mutation in the RB1 gene but also on the extent of inactivation ofthe first mutation.

The childhood eye cancer retinoblastoma is initiated by the loss of both allelesof the prototypic tumor suppressor gene, RB1. However, a large number of cytogenetic and comparative genomic hybridization (CGH) studies have shown that these M1 and M2 mutational events--although necessary for initiation--are not the only genomic changes in retinoblastoma. Some of these subsequent changes, which we have termed M3 to Mn, are likely crucial for tumor progression not only in retinoblastoma but also in other cancers. Moreover, genes showing genomic changein cancer are more stable markers and, therefore, possible therapeutic targets than genes simply differentially expressed. In this review, we provide the firstcomprehensive summary of the genomic evidence implicating gain of 1q, 2p, 6p, and 13q, and loss of 16q in retinoblastoma oncogenesis, including karyotype, CGH, and microarray CGH data. We discuss the search for candidate oncogenes and tumor suppressor genes within these regions, including the candidates (KIF14, MDM4, MYCN, E2F3, DEK, CDH11, and others), plus associations between genomic changes and clinical parameters. We also review studies of other regions of the retinoblastoma genome, the epigenetic changes of aberrant methylation of MGMT, RASSF1A, CASP8, and MLH1, and the roles microRNAs might play in this cancer. Although many candidate genes have yet to be functionally validated in retinoblastoma, work in this field lays out a molecular cytogenetic pathway of retinoblastoma development. Candidate cancer genes carry diagnostic, prognostic,and therapeutic implications beyond retinoblastoma.

Analysis of hereditary and nonhereditary retinoblastoma led to the formulation of the two-hit hypothesis of cancer in the early 1970s. The two-hit hypothesis was validated in the 1980s when both copies of the RB1 gene were shown to be mutatedin hereditary and nonhereditary retinoblastoma. However, consistent genetic abnormalities other than RB1 mutations suggest that additional events may be required for the formation of these malignant tumors. For example, MYCN amplification has long been known to occur in both retinoblastoma and neuroblastoma tumors and is strongly associated with poor prognosis in neuroblastoma. The DEAD box gene, DEAD box 1 (DDX1), is often coamplified with MYCN in both these childhood tumors. Here, we examine possible roles for DDX1 overexpression in retinoblastoma and neuroblastoma.

Approximately 30% of the cases of retinoblastoma (RB), the childhood eye cancer,are inherited and are manifested by unilateral or bilateral tumor. In sporadic tumors, accounting for 70% of cases, only one eye is affected. RB has three histological features: undifferentiated anaplastic cells, retinoblast pattern, and differentiated pattern characterized by Flexner Wintersteiner rosettes (FWR). Currently, results concerning phosphoprotein RB (pRB) expression in RB tumors are contradictory. In this study we detected pRB immunohistochemically in 10 tumors from bilateral or unilateral RBs, which did not show gross chromosomal alterations in cytogenetic studies. Interestingly, pRB was undetectable in only one tumor where we found distinct histological features. Our results suggest that pRB immunopositivity may be common in these tumors. However, it does not rule out the possibility that pRB is functionally inactive in some cases. This may be dueto the protein being present in phosphorylated form or being altered by point mutations not affecting its expression. Another possibility is that mechanisms other than RB1 gene changes may lead to retinoblastoma because not ALL cases of retinoblastoma show gene alterations. Together these findings may be useful in understanding the molecular mechanisms associated with this type of pediatric tumor.

Knudson's two-hit hypothesis proposes that two genetic changes in the RB1 gene are the rate-limiting steps of retinoblastoma. In the inherited form of this childhood eye cancer, only one mutation emerges during somatic cell divisions while in sporadic cases, both alleles of RB1 are inactivated in the growing retina. Sporadic retinoblastoma serves as an example of a situation in which twomutations are accumulated during clonal expansion of a cell population. Other examples include evolution of resistance against anticancer combination therapy and inactivation of both alleles of a metastasis-suppressor gene during tumor growth. In this article, we consider an exponentially growing population of cells that must evolve two mutations to (i) evade treatment, (ii) make a step toward (invasive) cancer, or (iii) display a disease phenotype. We calculate the probability that the population has evolved both mutations before it reaches a certain size. This probability depends on the rates at which the two mutations arise; the growth and death rates of cells carrying none, one, or both mutations; and the size the cell population reaches. Further, we develop a formula for the expected number of cells carrying both mutations when the final population size is reached. Our theory establishes an understanding of the dynamics of two mutations during clonal expansion.

Retinoblastoma (Rb), the most common intraocular tumor in childhood, is caused by the loss of function of both retinoblastoma susceptibility gene (RB1 or Rb1) alleles. In 1971, Alfred Knudson proposed his "two-hit" theory based upon empiric observations of the clinical genetics of Rb, revealing the role of tumor-suppressor genes in human cancer. Knudson proposed that: "In the dominant inherited form of Rb, one mutation is inherited via germ line and the second occurs in somatic cells. In the nonhereditary form, both mutations occur in somatic cells." The Knudson hypothesis was validated later with the cloning of RB1, the first tumor-suppressor gene to be identified. A few years later, Harbour extended these findings to small-cell lung cancer, showing that the RB1 locus was disrupted in tumors other than Rb and osteosarcoma. Since then, it has been found that most, if not all, tumors have defects in their RB1 pathway through genetic lesions in the RB1 gene itself or other genes in the pathway. The history of Rb research highlights how basic research on a rare childhood cancer can have a much broader effect on a disease that affects millions of people each year worldwide.

The retinoblastoma gene (RB) is the prototype of a class of genes, called tumor suppressor genes, for which loss-of-function mutations are oncogenic. Such geneswould then normally function to suppress or prevent tumor formation. Classical genetic and cytogenetic studies of retinoblastoma, a rare childhood eye cancer, laid a fundamental groundwork for the molecular cloning of this gene. Surprisingly, mutations of RB are found not only in retinoblastomas but also in some osteosarcomas, soft-tissue sarcomas, and carcinomas of breast, lung, prostate or bladder, suggesting a broad role for RB in human oncogenesis. In support of this hypothesis, a wild-type copy of RB is able to suppress the neoplastic properties of several types of tumor cells with mutated endogenous RBalleles. The RB gene product, pp110RB, is a nuclear phosphoprotein with DNA binding activity. RB protein is cyclically phosphorylated and dephosphorylated during the cell division cycle, and may play a significant role in its regulation.

BACKGROUND: Retinoblastoma (RB) is a childhood ocular malignancy associated withmutations in RB1, a tumor susceptibility gene. Inactivation of both copies of the RB1 gene in a retinal cell is followed by the sequential acquisition of additional genetic changes that define the course to tumor formation. METHODS: To identify the genetic events that cooperate with loss of the RB1 gene function, we performed a whole genome sampling assay based on single nucleotide polymorphism genotyping. We used DNA isolated from 25 sporadic, unilateral RB tumors and matched blood samples. RESULTS: Genomic profiles were analyzed to identify regions of loss of heterozygosity or amplification. Two major subclasses of RB tumors were defined by the presence (n = 18) or absence (n = 7) of loss of heterozygosity of chromosome 13. Loss of heterozygosity in most cases was the result of copy-neutral events caused by mitotic recombination and mitotic nondisjunction. tumors harbored novel regions of amplification at 1q44, 3p25, 11q14, 11q25, 14q23, 15q21, 16p13, 17p11.2, 19q13, and 20q13, whereas regions ofloss included 6q22, 7q21, and 21q2. CONCLUSION: Whole genome sampling assay-based analysis of unilateral RB tumors revealed novel regions as significant. These minimum critical regions that are lost or amplified are expected to harbor genesthat aid the process of tumorigenesis.

PURPOSE OF REVIEW: Retinoblastoma is a pediatric eye tumor that serves as a paradigm for understanding the genetic basis of cancer. This review will highlight recent advances in retinoblastoma genetic research and discuss how these new findings influence our knowledge of retinoblastoma tumorigenesis and management. RECENT FINDINGS: Current data demonstrate that retinomas, benign retinal tumors found in some retinoblastoma patients, exhibit bi-allelic mutations in RB1, the retinoblastoma gene, and lack of expression of the retinoblastoma protein. Interestingly, retinomas demonstrate a low level of genomic instability that becomes progressively more severe in retinoblastoma tumors. Additionally, a subset of retinomas share genomic alterations with retinoblastoma. Collectively, these data suggest that retinomas represent true premalignant lesions and not regressed retinoblastoma tumors, as previously thought. Translational advances in retinoblastoma genetic research include development of an allele-specific assay that now enables the identification of mutational mosaicism, thereby increasing the rate of RB1 mutation detection in bilaterally affected patients to as high as 95%. SUMMARY: These and related research efforts reveal novel data that enhance our understanding of the biologyof retinoblastoma. These observations may facilitate new therapeutic approaches to further decrease the morbidity and mortality associated with retinoblastoma and other more common forms of cancer.

BACKGROUND: Retinoblastoma is a neuroblastic tumor of childhood with an incidence of 1: 20 000. Retinoblastoma gene (Rb1) is a tumor suppressor gene that is located on the long arm of chromosome 13 at region 14. This study was to evaluate the constitutional monoallelic Rb1 deletion among retinoblastoma families. METHODS: Nine families with an affected Rb proband were evaluated. Clinical examination, pedigree analysis, and complete eye examination were given to patients, their sibs and parents. Standard cytogenetic and fluorescence in situ hybridization (FISH) analyses were carried out for ALL of them. Also, two sib fetuses were tested for Rb1 deletion. RESULTS: No dysmorphic features were detected in any patient. Developmental milestones were within normal limit except in one proband who had a mild delay. The age of onset ranged from one month to 4years. Positive family history was found in two families. In one, the father and3 sibs had retinoblastoma, and in the other, 2 sibs were affected, but the parents were free. Chromosomal study revealed no abnormalities in ALL parents and sibs. Two patients had mosaic chromosome 13 abnormalities, 46,XY/46,XY,del(13)(pter-->q14:) and 46,XX/46,inv(13)(q14q22). FISH analysis detected mosaic Rb1 deletion in two patients and excluded Rb1 deletion in two fetuses. CONCLUSIONS: The detection of genetic alterations affecting the Rb1 locus is important for the establishment of carriers, and prenatal and presymptomatic diagnosis. The search for deleted Rb1 mosaic cell lines is important for genetic counseling. Germline mutation may be considered as genetictransmission method of the Rb1 gene.

BACKGROUND: children diagnosed with retinoblastoma, a rare cancer of the eye, tend to develop and die of second primary cancers in childhood and adolescence, but few investigations have followed patients into adulthood. Retinoblastoma is frequently caused by inherited mutations of the RB1 tumor suppressor gene. Most patients with germline (hereditary) mutations have bilateral disease. PURPOSE: We sought to quantify the mortality from second malignancies among long-term survivors of retinoblastoma and to identify factors that predispose to these deaths. METHODS: A retrospective cohort study examined mortality among 1603 patients enrolled at 1 year after diagnosis of retinoblastoma during the period 1914-1984. Data on demography, family history, and retinoblastoma treatment werecollected by medical chart review and questionnaire interview. Number of deaths,by cause, was compared with the corresponding expected figure based on U.S. mortality data for the general population for 1925-1990. RESULTS: Follow-up was complete for 1458 patients (91%) for a median of 17 years after retinoblastoma diagnosis. A total of 305 deaths occurred, 167 of them from retinoblastoma. There were 96 deaths from second primary tumors (relative risk [RR] = 30), 21 from other known causes (RR = 1.0), and 21 from ill-defined or unknown causes. Statistically significant excess mortality was found for second primary cancers of bone, connective tissue, and malignant melanoma and benign and malignant neoplasms of brain and meninges. Among 919 children with bilateral retinoblastoma, 90 deaths from second primary tumors occurred (RR = 60). Deaths from second tumors were more frequent among females (RR = 39) than males (RR = 22) (P = .007). The cumulative probability of death from second primary neoplasms was 26% at 40 years after bilateral retinoblastoma diagnosis, and additional cancer deaths occurred thereafter. Radiotherapy for retinoblastoma further increased the risk of mortality from second neoplasms. An excess of mortality from a second cancer, not seen in prior studies, was found among the 684 children with unilateral disease (RR = 3.1; 95% confidence interval = 1.0-7.3). CONCLUSIONS: These findings implicate germinal mutations in the retinoblastoma gene in second cancer mortality. Radiotherapy treatment for retinoblastoma appears to further enhance the inborn susceptibility to development of a second cancer. IMPLICATIONS: Patients with retinoblastoma, particularly bilateral retinoblastoma, should have careful follow-up, and interventions should be developed to reduce mortality from a second cancer.

Pancreatoblastomas are unusual malignant neoplasms of the pediatric pancreas that may also rarely affect adults. The molecular pathogenesis of pancreatoblastomas is unknown. They are clinicopathologically distinct from adult pancreatic ductaladenocarcinomas, but their occasional occurrence in patients with Beckwith-Wiedemann syndrome and the case presented here of a pancreatoblastoma in an adult patient with familial adenomatous polyposis (FAP) suggests that they might bear a genetic similarity to other infantile embryonal tumors such as hepatoblastomas. We analyzed a series of nine pancreatoblastomas for mutations common to other embryonal malignancies including somatic alterations in the adenomatous polyposis coli (APC)/beta-catenin pathway and chromosome 11p, using immunohistochemistry for beta-catenin, 5q and 11p allelic loss assays, and direct DNA sequencing of exon 3 of the beta-catenin gene and the mutation cluster region of the APC gene. In addition, we analyzed the pancreatoblastomas for alterationsfound in adult-type pancreatic ductal adenocarcinomas including mutations in theK-ras oncogene and the p53 and DPC4 tumor suppressor genes, using direct DNA sequencing of exon 1 of K-ras and immunohistochemistry for p53 and Dpc4. Allelicloss on chromosome 11p was the most common genetic alteration in pancreatoblastomas, present in 86% (six of seven informative cases). Molecular alterations in the APC/beta-catenin pathway were detected in 67% (six of nine), including five neoplasms with activating mutations of the beta-catenin oncogene and the one FAP-associated tumor with biallelic APC inactivation (germline truncating mutation combined with loss of the wild-type allele); seven neoplasmsshowed abnormal nuclear accumulation of beta-catenin protein. In contrast, loss of Dpc4 protein expression was present in only two cases (one diffuse and one focal), and no alterations in the K-ras gene or p53 expression were detected. Our findings indicate that pancreatoblastomas are genetically distinct from the morecommon pancreatic ductal adenocarcinomas, but bear a close molecular pathogenesis to hepatoblastomas. In addition, pancreatoblastoma may represent an extracolonicmanifestation of FAP.

The cyclin-dependent kinase inhibitor p16(INK4A) is frequently inactivated in childhood T-cell acute lymphoblastic leukemia. To investigate possible consequences of this genetic alteration for tumor development, we conditionally expressed p16(INK4A) in the T-cell acute lymphoblastic leukemia line CCRF-CEM, which carries a homozygous deletion of this gene. In agreement with its reportedfunction, p16(INK4A) expression was associated with hypophosphorylation of the retinoblastoma protein pRB and stable cell cycle arrest in G(0)/G(1), documenting that the pRB/E2F pathway is functional in these cells. Unexpectedly, p16(INK4A) expression increased the sensitivity threshold for glucocorticoid (GC)-induced apoptosis from therapeutic to physiologic levels. As a possible explanation for this phenomenon, we found that p16(INK4A)-arrested cells had elevated GC receptor expression associated with enhanced GC-mediated transcriptional activity and increased responsiveness of the GC-regulated cyclin D3 gene. These data are supported by our previous findings that GC receptor levels critically influence GC sensitivity and imply that p16(INK4A) inactivation, in addition to allowing unrestricted proliferation, represents a mechanism by which lymphoid tumor cellsmight escape cell death triggered by endogenous GC.

The understanding of the molecular biology of human cancer has advanced rapidly in the last decade, in part due to discoveries in the rare, pediatric ocular tumor, retinoblastoma. RB studies have led to recognition of a class of human genes, the tumor suppressor genes, that are critical in the initiation and progression of the malignant process. mutations in the RB1 gene initiate RB and other specific tumors. They may also contribute to progressive stages of many other malignancies. The protein product of RB1 (p110RB1) is a basic regulator ofthe cell cycle. In the absence of normal protein, the cell proceeds to the next cell division without the potential to become quiescent. Understanding the genetics of RB has benefited the patients, as the precise identification of the RB1 mutations in families has led to accurate prediction of individuals at risk for RB tumors. It seems unlikely, in the foreseeable future, that direct geneticmanipulation of mutant RB1 genes will play a role in therapy, but complete understanding of the function of p110RB1 may eventually allow exploitation of its powerful antiproliferative effect. Other molecular genetic events in addition toRB1 mutations are documented in RB tumors, and may play a critical role in the full malignant phenotype. The oncogene, N-myc, is amplified in some RB tumors and is expressed in normal fetal retina. The cytogenetic abnormality, i(6p), is almost unique to RB tumors. The molecular and tissue-specific roles of these abnormalities are not yet known. Many RB tumors also acquire excessive expression of the cell surface membrane glycoprotein, p170, linked to multidrug resistance,whether or not the RB tumor has been exposed to chemotherapy. We anticipate thatways to avoid or counteract the drug resistance of excessive p170 expression will be developed for other pediatric tumors and eventually will be applied to chemotherapy for RB patients.

BTI - GeneReviews#. Retinoblastoma (Rb) is a malignant tumor of the developing retina that occurs inchildren, usually before age five years. Rb occurs in cells that have cancer-predisposing mutations in both copies of the gene RB1. Rb may be unifocalor multifocal. About 60% of affected individuals have unilateral Rb with a mean age of diagnosis of 24 months; about 40% have bilateral Rb with a mean age of diagnosis of 15 months. Individuals heterozygous for a cancer-predisposing mutation in one RB1 allele are said to have a germline mutation and thus have a heritable predisposition to Rb. They also have an increased risk of developing non-ocular tumors. The clinical diagnosis of retinoblastoma is usually established by examination of the fundus of the eye using indirect ophthalmoscopy. Imaging studies can be used to support the diagnosis and stage the tumor. RB1 is the only gene in which mutations are known to cause heritable predisposition to retinoblastoma. Molecular genetic testing of RB1 in white blood cell DNA can identify a germline mutation in more than 95% of individuals with aheritable predisposition to Rb. The probability that an RB1 gene mutation will be detected in white blood cell DNA of an index case depends on whether the tumor is bilateral or unilateral, whether the family history is positive or negative, andthe sensitivity of the testing methodology. Treatment of manifestations: Early diagnosis and treatment of Rb and non-ocular tumors can reduce morbidity and increase longevity; care is best provided by multidisciplinary teams of specialists including ophthalmology, pediatric oncology, pathology, and radiation oncology. Treatment options depend on tumor stage, number of tumor foci (unifocal, unilateral multifocal, or bilateral), localization and size of the tumor(s) within the eye, presence of vitreous seeding, and age of the child. Treatment options include enucleation; cryotherapy; laser, systemic, or local ocular chemotherapy combined with or followed by laser or cryotherapy; radiationtherapy using episcleral plaques; and, as a last resort, external beam radiotherapy. Prevention of secondary manifestations: If possible, any radiation(including x-ray, CT scan, and external beam radiation) should be avoided in individuals with heritable Rb to minimize the lifetime risk of developing late-onset second cancers. Surveillance: For early detection of Rb tumor foci inchildren at risk (i.e., those with: (1) an RB1 germline mutation [based either on molecular genetic testing or past history of bilateral or multifocal tumors], (2) a history of unilateral retinoblastoma, (3) one or more retinomas, and/or (4) a positive family history but unknown mutation status), an eye examination every three to four weeks until age one year and then less frequently until age three years is recommended. Clinic examinations with cooperative children are performed every three to six months until age seven years, then annually and eventually biannually for life. Young and/or uncooperative children usually require examination under anesthesia. To detect second non-ocular tumors in individuals with retinoblastoma, physicians and parents should promptly evaluate complaints of bone pain or lumps because of the high risk for sarcomas and other cancers; however, effective screening protocols have not yet been developed. Agents/circumstances to avoid: Limiting exposures to DNA-damaging agents (radiation, tobacco, and UV light) may reduce the excess cancer risks in survivors of heritable retinoblastoma. Evaluation of relatives at risk: Molecular genetic testing for early identification of asymptomatic at-risk children in a family reduces the need for costly screening procedures in those at-risk family members who have not inherited the disease-causing mutation. Heritable predisposition to retinoblastoma is caused by germline mutations in RB1 and is transmitted in an autosomal dominant manner. The risks to family members of a proband with Rb depend on whether or not the proband has a germline RB1 mutation. Molecular genetic testing of DNA from the proband's white blood cells (or other non-tumorous cells), as well as from the tumor, may detect the cancer-predisposing RB1 mutation. If a cancer-predisposing RB1 mutation is identified in the proband's white blood cells, mutation analysis can clarify thegenetic status of at-risk sibs and offspring. If RB1 molecular genetic testing is not available or is uninformative, indirect testing using polymorphic loci linked to RB1 can be used in familial Rb to estimate the genetic status of at-risk family members. Empiric recurrence risk estimates can be used in families in which molecular genetic testing of RB1 and linkage analysis are unavailable or uninformative. Prenatal testing is possible if the heritable RB1 mutation in theparent is known or if RB1 linkage analysis is informative in the family.#CI- Copyright (c) 1993-2013, University of Washington, Seattle. ALL rights reserved.#FED - Pagon, Roberta A#ED- Pagon RA#FED - Adam, Margaret P#ED- Adam MP#FED - Bird, Thomas D#ED- Bird TD#FED - Dolan, Cynthia R#ED- Dolan CR#FED - Fong, Chin-To#ED- Fong CT#FED - Stephens, Karen#ED- Stephens K#FAU - Lohmann, Dietmar R

BACKGROUND: Human osteosarcoma is the most common pediatric bone tumor. There islimited understanding of the molecular mechanisms underlying osteosarcoma oncogenesis, and a lack of good diagnostic as well as prognostic clinical markers for this disease. Recent discoveries have highlighted a potential role of a number of genes including: RECQL4, DOCK5, SPP1, RUNX2, RB1, CDKN1A, P53, IBSP, LSAMP, MYC, TNFRSF1B, BMP2, HISTH2BE, FOS, CCNB1, and CDC5L. METHODS: Our objective was to assess relative expression levels of these 16 genes as potential biomarkers of osteosarcoma oncogenesis and chemotherapy response in human tumors. We performed quantitative expression analysis in a panel of 22 human osteosarcoma tumors with differential response to chemotherapy, and 5 normal human osteoblasts. RESULTS: RECQL4, SPP1, RUNX2, and IBSP were significantly overexpressed, and DOCK5, CDKN1A, RB1, P53, and LSAMP showed significant loss ofexpression relative to normal osteoblasts. In addition to being overexpressed inosteosarcoma tumor samples relative to normal osteoblasts, RUNX2 was the only gene of the 16 to show significant overexpression in tumors that had a poor response to chemotherapy relative to good responders. CONCLUSION: These data underscore the loss of tumor suppressive pathways and activation of specific oncogenic mechanisms associated with osteosarcoma oncogenesis, while drawing attention to the role of RUNX2 expression as a potential biomarker of chemotherapy failure in osteosarcoma.

The RB1 gene was cloned because its inactivation causes the childhood ocular tumor, retinoblastoma. It is widely expressed, inactivated in most human malignancies, and present in diverse organisms from mammals to plants. Initially, retinoblastoma protein (pRB) was linked to cell cycle regulation, but it also regulates senescence, apoptosis, autophagy, differentiation, genome stability, immunity, telomere function, stem cell biology, and embryonic development. In the 23 years since the gene was cloned, a formal international symposium focused on the RB pathway has not been held. The "First International RB tumor Suppressor Meeting" (Toronto, Canada, November 19-21, 2009) established a biennial event tobring experts in the field together to discuss how the RB family ("pocket proteins"), as well as its regulators and effectors, influence biology and humandisease. We summarize major new breakthroughs and emerging trends presented at the meeting.

To assess complete remission before subjecting nongermline metastatic retinoblastoma patients to an autologous peripheral stem cell transplant, we tested for patient-specific retinoblastoma tumor suppressor gene (RB1) mutant alleles in cerebrospinal fluid (CSF) and bone marrow. In 1 child with CSF and 1 with bone marrow metastases, allele-specific polymerase chain reaction (AS-PCR) detected the biallelic RB1 mutations specific to their tumors. The tumor of child A was homozygous for R251X, and in child B, it was homozygous for R358X. In child A, the R251X mutation was detected in mutant controls diluted to 1:12,800 but not in CSF samples, corroborating clinical remission after chemotherapy. In child B's bone marrow, AS-PCR for R358X was strongly positive at the detection of relapse,and subsequent bone marrow samples corroborated clinical remission after chemotherapy. No mutant tumor RB1 alleles were detected in their harvested peripheral blood stem cells. Both children were deemed suitable candidates for supralethal-dosage consolidation chemotherapy followed by autologous peripheral stem cell rescue of the bone marrow aimed at curing their metastatic retinoblastoma. When child A recurred, the mutant tumor RB1 allele was detected 3.5 months before conventional pathology detected retinoblastoma tumor cells in the CSF. Assaying tumor-specific RB1 mutations complements cytological and immunohistochemical assessment of retinoblastoma involvement of CSF and bone marrow. tumor cells can be detected in numbers lower than possible by conventional methods. An early diagnosis of relapse may allow an early institution of new therapy. A prospective international multicenter trial of therare patients with metastatic retinoblastoma would assess the role of molecular monitoring in surveillance for minimal residual disease and recurrence.#CI- Copyright (c) 2010 Mosby, Inc. ALL rights reserved.

PURPOSE: The retinoblastoma gene (RB1) is a tumor suppressor gene that was firstdiscovered in a rare ocular pediatric tumor called retinoblastoma (RB). The RB1 gene is essential for normal progression through the cell cycle and exerts part of its function through the family of transcription factors (E2F) and many otherintermediaries. In the absence of normal RB1, genomic instability and chromosomal aberrations accumulate, leading to tumor initiation, progression, and ultimatelymetastasis. The purpose of this report was to identify the molecular pathways that are deregulated in retinoblastoma. METHODS: We compared gene expression signatures of matched normal retinal tissue and retinoblastoma (RB) tumor tissuefrom six individuals, using microarray analysis followed by statistical and bioinformatic analyses. RESULTS: We identified 1,116 genes with increased expression and 837 with decreased expression in RB tumor tissue compared to matched normal retinal tissue. Functional categories of the cognate genes with the greatest statistical support were cell cycle (309 genes), cell death (437 genes), DNA replication, recombination and repair (270 genes), cellular growth and proliferation (464 genes), and cellular assembly and organization (110 genes). The list included differentially expressed retinal cone-cell-specific markers. These data indicated the predominance of cone cells in RB and support the idea that the latter group of cells may be the cells of origin for RB. CONCLUSIONS: The genes differentially expressed in RB as compared to normal retina belong mainly to DNA damage-response pathways, including, but not limitedto, breast cancer associated genes (BRCA1, BRCA2), ataxia telangiectasia mutatedgene (ATM), ataxia telangiectasia and Rad3 related gene(ATR), E2F, checkpoint kinase 1 (CHK1) genes. In addition, novel pathways, such as aryl hydrocarbon receptor (AHR) signaling, polo-like kinase and mitosis, purine metabolism pathways were involved. The molecules AHR, CHK1, and polo-like kinases are of particular interest because there are several currently available drugs that target these molecules. Further studies are needed to determine if targeting these pathways in RB will have therapeutic value. It is also important to evaluate the relative importance of these pathways in different cells that make up the normal retina.

Retinoblastoma is a pediatric eye tumor that serves as a paradigm for understanding the genetic basis of cancer. mutations and/or epigenetic alterations inactivating both alleles of the retinoblastoma gene (RB) are associated with retinoblastoma. There are many other genes which express differentially in the preneoplastic retinal cells after RB loss, as cells progress to form tumors. These genetic changes and the pathways involved can provide valuable insight into the development and progression of this cancer. Conventional molecular and genetic methods for studying cancer are limited to the analysis of one locus at a time. A cluster of genes that are regulated together can be identified by DNA microarray, and the functional relationships can uncover new aspects of cancer biology. Meta analysis is an important tool for the identification and validation of differentially expressed genes to increase power in clinical and biological studies across different sets of data. Recently, metaanalysis approaches have been applied to large collections of microarray datasets to investigate molecular commonalities of multiple cancer types not only to findthe common molecular pathways in tumor development but also to compare the individual datasets to other cancer datasets to identify new sets of genes. The outcome of these analyses might accelerate the application of basic research findings into daily clinical practice through translational research and may have an impact on foreseeing the clinical outcome, predicting tumor response to specific therapy, identification of new prognostic biomarkers, discovering targets for the development of novel therapies and providing further insights. These and related research efforts reveal novel data that enhance our understanding of the biology of retinoblastoma. These observations may facilitate new therapeutic approaches to further decrease the morbidity and mortality associated with retinoblastoma and other more common forms of cancer.#CI- Copyright (c) 2010. Published by Elsevier B.V.

pediatric rhabdomyosarcoma occurs as two biologically distinct histological variants, embryonal (ERMS) and alveolar (ARMS). To identify genomic changes thatdrive ERMS pathogenesis, we used a new array comparative genomic hybridization (aCGH) platform to examine a specific subset of ERMS tumors, those occurring in children with clinically defined intermediate-risk disease. The aCGH platform used has an average probe spacing approximately 1 kb, and can identify genomic changes with single gene resolution. Our data suggest that these tumors share a common genomic program that includes inactivation of a master regulator of the p53 and Rb pathways, CDKN2A/B, and activation of FGFR4, Ras, and Hedgehog (Hh) signaling. The CDKN2A/B tumor suppressor is deleted in most patient samples. FGFR4, which encodes a receptor tyrosine kinase, is activated in 20% of tumors, predominantly by amplification of mutant, activating FGFR4 alleles. Over 50% of patients had low-level gains of a region containing the Hh-pathway transcriptionfactor GLI1, and a gene expression pattern consistent with Hh-pathway activation. We also identified intragenic deletions affecting NF1, a tumor suppressor and inhibitor of Ras, in 15% of tumor samples. Deletion of NF1 and the presence of activating Ras mutations (in 42% of patients) were mutually exclusive, suggesting NF1 loss is an alternative and potentially common mechanism of Ras activation inERMS. Our data suggest that intermediate-risk ERMS is driven by a common set of genomic defects, a finding that has important implications for the application of targeted therapies to improve the treatment of children diagnosed with this disease.#CI- Copyright (c) 2011 Wiley-Liss, Inc.

Oligonucleotide array comparative genomic hybridization, karyotype and fluorescence in situ hybridization analyses were employed to delineate the cytogenetic abnormalities in a case of pediatric acute megakaryoblastic leukemia. Here we present a unique genetic profile that includes bi-allelic deletions within 13q14, where the retinoblastoma tumor suppressor gene (RB1) resides, as well as isolated trisomy 21 without a concomitant mutation in the hematopoietic transcription factor GATA1s and translocation (17;22), that does not involve themegakaryoblastic leukemia 1 (MKL1) gene located on chromosome 22. Alteration of the RB1 gene is most likely the critical leukemogenic event in this patient.#CI- Copyright (c) 2011 Wiley-Liss, Inc.

PURPOSE: Retinoblastoma (RB), the most common intraocular tumor occurring in infancy and early childhood, is most often related to mutations in the RB1 gene.In this study, we screened the RB1 germline mutations in 41 unrelated Moroccan patients with retinoblastoma, 25 heritable cases, and 16 sporadic unilateral cases. METHODS: After complete ophthalmic examinations were performed and consent obtained, DNA was extracted from peripheral blood, and screening of RB1 mutations was performed with PCR direct sequencing of the promoter and the 27 coding exonsof the RB1 gene. RESULTS: We identified ten germline mutations in 10/41 (24.39%)unrelated patients, among which three had not been previously reported. The mutation detection rate was 40% (10/25) in the heritable cases and 0% (0/16) in the sporadic unilateral cases. Of these mutations, six were nonsense, and three were frameshifts, ALL associated with severe phenotypes resulting in bilateral and multifocal tumors. One splice site mutation was found in a familial case associated with a low expressivity phenotype resulting in unilateral and unifocal tumors. Moreover, eight intronic variants were identified, three of which were novel. CONCLUSIONS: This first report of RB1 gene screening in Moroccan patientswith retinoblastoma shows a comparable mutational spectrum to those reported previously, which has evident importance for managing patients with retinoblastoma and their families.

Retinoblastoma is an aggressive childhood cancer of the developing retina that is initiated by the biallelic loss of RB1. tumours progress very quickly following RB1 inactivation but the underlying mechanism is not known. Here we show that the retinoblastoma genome is stable, but that multiple cancer pathways can be epigenetically deregulated. To identify the mutations that cooperate with RB1 loss, we performed whole-genome sequencing of retinoblastomas. The overall mutational rate was very low; RB1 was the only known cancer gene mutated. We then evaluated the role of RB1 in genome stability and considered non-genetic mechanisms of cancer pathway deregulation. For example, the proto-oncogene SYK is upregulated in retinoblastoma and is required for tumour cell survival. Targeting SYK with a small-molecule inhibitor induced retinoblastoma tumour cell death in vitro and in vivo. Thus, retinoblastomas may develop quickly as a result of the epigenetic deregulation of key cancer pathways as a direct or indirect result ofRB1 loss.

Retinoblastoma is a pediatric retinal tumor initiated by biallelic inactivation of the retinoblastoma gene (RB1). RB1 was the first identified tumor suppressor gene and has defined roles in the regulation of cell cycle progression, DNA replication, and terminal differentiation. However, despite the abundance of work demonstrating the molecular function and identifying binding partners of pRb, the challenge facing molecular biologists and clinical oncologists is how to integrate this vast body of molecular knowledge into the development of targetedtherapies for treatment of retinoblastoma. We propose that a more thorough genetic understanding of retinoblastoma would inform targeted treatment decisions and could improve outcomes and quality of life in children affected by this disease.

Retinoblastoma is a pediatric cancer that has served as a paradigm for tumor suppressor gene function. Retinoblastoma is initiated by RB gene mutations, but the subsequent cooperating mutational events leading to tumorigenesis are poorlycharacterized. We investigated what these additional genomic alterations might be using human retinoblastoma samples and mouse models. Array-based comparative genomic hybridization studies revealed deletions in the CDKN2A locus that include ARF and P16INK4A, both of which encode tumor suppressor proteins, in both human and mouse retinoblastoma. Through mouse genetic analyses, we found that Arf was the critical tumor suppressor gene in the deleted region. In mice, inactivation of one allele of Arf cooperated with Rb and p107 loss to rapidly accelerate retinoblastoma, with frequent loss of heterozygosity (LOH) at the Arf locus. Arfhas been reported to exhibit p53-independent tumor suppressor roles in other systems; however, our results showed no additive effect of p53 and Arf coinactivation in promoting retinoblastoma. Moreover, p53 inactivation completely eliminated any selection for Arf LOH. Thus, our data reveal important insights into the p53 pathway in retinoblastoma and show that Arf is a key collaborator with Rb in retinoblastoma suppression.

PURPOSE: To report on a novel translocation related to a suprasellar primitive neuroectodermal tumor (sPNET) and retinoblastoma. DESIGN: Case report. METHODS: A 6-year-old girl underwent genetic testing after developing unilateral retinoblastoma subsequent to treatment (surgery, chemotherapy, and stem-cell rescue) for a sPNET found at 1 year of age. RESULTS: Genetic testing found the girl's karyotype to be 46,XX,t(11;13)(q21;q14.2); a novel translocation not previously reported in patients with either retinoblastoma or sPNET. CONCLUSIONS: Our patient had a novel translocation affecting the retinoblastoma 1 (RB1) gene,46,XX,t(11;13)(q21;q14.2) resulting in the late development of unilateral retinoblastoma. Although she only developed unilateral retinoblastoma, her central nervous system was affected at a very early age. How her complex mutation resulted in retinoblastoma and antecedent sPNET remains unknown.

Primary cancers of the eye are rare. These include uveal melanoma, a tumor that preferentially affects the choroid of light-eyed, fair-skinned Europeans, and the pediatric retinal neoplasm retinoblastoma, which is slightly more common worldwide. Uveal melanoma kills about half of affected patients. Most succumb tohepatic metastases, which are unresponsive to current therapy. Factors indicative of poor prognosis include tumor size, ciliary body involvement, epithelioid cells, extraocular extension, lymphocytic and melanophagic infiltration, mitoticactivity, vascular mimicry patterns, and most importantly, the detection of monosomy 3 and class 2 gene expression profile in tumor cells using special tests. Most retinoblastomas are caused by sporadic somatic mutations in the RB1 gene, but about one-third arise in infants with germline mutations. The latter tend to develop earlier, are often bilateral and are transmissible to offspring as an autosomal dominant trait. Retinoblastoma displays varying degrees of differentiation including Homer Wright and Flexner-Wintersteiner rosettes and photoreceptor differentiation (fleurettes). Rosettes are more common in eyes enucleated from very young infants. tumors composed entirely of fleurettes (retinoma/retinocytoma) are thought to be retinoblastoma precursors, and like retinoblastoma, harbor mutations in both copies of the RB1 gene. Retinoblastoma is a major cancer treatment success story in developed countries where most deaths are caused by secondary tumors in germline mutation carriers. High-risk histopathological features that are an indication for adjuvant chemotherapy include massive uveal invasion and retrolaminar optic nerve invasion. Eye-sparing therapies including brachyradiotherapy and systemic and intra-arterial chemotherapy have reduced the number of eyes with retinoblastoma requiring enucleation in recent years.

Retinoblastoma (RB), a childhood neoplasia of the retinoblasts, can occur unilaterally or bilaterally, with one or multiple foci per eye. RB is associatedwith somatic loss of function of both alleles of the tumor suppressor gene RB1. Hereditary forms emerge due to germline loss of function mutations in RB1 alleles. RB has long been the prototypic "model" cancer ever since Knudson's "two-hit" hypothesis. However, a simple two-hit model for RB is challenged by anincreasing number of studies documenting additional hits that contribute to RB development. Here we review the genetics and epigenetics of RB with a focus on the role of small non-coding RNAs (microRNAs) and on novel findings indicating the relevance of DNA methylation in the development and prognosis of this neoplasia. Studies point to an elaborated landscape of genetic and epigenetic complexity, in which a number of events and pahtways play crucial roles in the origin and prognosis of RB. These include roles for microRNAs, inprinted loci, and parent-of-origin contributions to RB1 regulation and RB progression. This complexity is also manifested in the structure of the RB1 locus itself: it includes numerous repetitive DNA segments and retrotransposon insertion elements, some of which are actively transcribed from the RB1 locus. Altogether, we conclude that RB1 loss of function represents the tip of an iceberg of events that determine RB development, progression, severity, and disease risk. Comprehensive assessment of personalized RB risk will require genetic and epigenetic evaluations beyond RB1 protein coding sequences.

Abstract Background: Retinoblastoma (RB) is the most common primary childhood intraocular malignancy and usually presents before the age of 4 years. RB in late childhood is rare and may pose a diagnostic challenge to clinicians. Materials and Methods: Patients over the age of 4 years with RB were identified retrospectively. Clinical data, histological findings, and molecular genetic diagnoses were obtained. Results: Two cases of late onset RB were identified. Case 1 was a 10-year-old boy who presented with floaters, and was found to have a unilateral exudative retinal detachment and RB on clinical examination. Genetic testing showed a novel homozygous mutation in exon 20 of the RB1 gene in the tumor sample, c.2027_2034dup, resulting in p.Ile679X. No mutation was found in the DNA obtained from the peripheral blood sample. Case 2 was a 6-year-old boy who presented with loss of vision and pain in the left eye. RB was diagnosed on clinical examination with exudative retinal detachment. Genetic testing showed no mutation in the RB1 gene, but complete methylation of the RB1 promoter region. Conclusions: RB can rarely present in late childhood. Clinicians should considerRB as a diagnosis when faced with a patient with unexplained exudative retinal detachment.

ABSTRACT Background: Retinoblastoma is a hereditary cancer of childhood caused by mutations in the RB1 tumor suppressor gene. An early diagnosis is critical for survival and eye preservation, thus identification of RB1 mutations is importantfor unequivocal diagnosis of hereditary retinoblastoma and risk assessment in relatives. Methods: We studied 144 families for 20 years, performing methodological changes to improve detection of mutation. Segregation analysis ofpolymorphisms, MLPA, FISH and cytogenetic assays were used for detection of "at risk haplotypes" and large deletions. Small mutations were identified by heteroduplex/DNA sequencing. Results: At risk haplotypes were identified in 11 familial and 26 sporadic cases, being useful for detection of asymptomatic carriers, risk exclusion from relatives and uncovering RB1 recombinations. Ten large deletions (eight whole gene deletions) were identified in six bilateral/familial and four unilateral retinoblastoma cases. Small mutations were identified in 29 cases (four unilateral retinoblastoma patients), being the majority nonsense/frameshift mutations. Genotype-phenotype correlations confirm that the retinoblastoma presentation is related to the type of mutation, but some exceptions may occur and it is crucial to be considered for genetic counseling. Three families included second cousins with retinoblastoma carrying different haplotypes, which suggest independent mutation events. Conclusion: This study enabled us to obtain information about molecular and genetic features of patients with retinoblastoma in Argentina and correlate them to their phenotype.

INTRODUCTION: Retinoblastoma is a childhood cancer of the retina originated by altered or null retinoblastoma protein (pRb) expression. Genetic alterations in both RB1 alleles in the retinal cells are required for the development of retinoblastoma. In the sporadic form, non-hereditary RB1 gene mutations take place in a single retinoblast cell, and are therefore only present in tumor DNA (somatic mutations). Sporadic retinoblastoma is primarily unilateral, lacks family history and has no risk of transmission to descendants. Genetic tests fordetection of RB1 mutation has improved the identification of carriers and facilitated accurate genetic counseling. OBJECTIVE: To identify mutations in theRB1 gene in Colombian patients with sporadic retinoblastoma by PCR-SSCP followedby sequence. MATERIALS AND METHODS: Four patients with sporadic retinoblastoma were analyzed by PCR-SSCP, followed by DNA sequencing to identify variations in the RB1 gene. RESULTS: We identified five variations in RB1 gene: three new mutations (one germline and two somatic mutations), one new polymorphism and onealready reported somatic mutation. Four mutations were found in three patients with unilateral retinoblastoma and one mutation was found in a patient with bilateral retinoblastoma. One of these was a germline mutation in a sporadic unilateral retinoblastoma that was not present in the parents or three siblings analyzed. CONCLUSIONS: Our results emphasize the importance of identifying mutations for genetic counseling and clinical management of sporadic retinoblastoma patients. Description of a new RB1 gene variant is interesting since there have been a small number of polymorphisms reported for this gene.

Genetically engineered mouse models (GEMMs) of human cancer are important for advancing our understanding of tumor initiation and progression as well as for testing novel therapeutics. Retinoblastoma is a childhood cancer of the developing retina that initiates with biallelic inactivation of the RB1 gene. GEMMs faithfully recapitulate the histopathology, molecular, cellular, morphometric, neuroanatomical and neurochemical features of human retinoblastoma. In this study, we analyzed the genomic and epigenomic landscape of murine retinoblastoma and compared them to human retinoblastomas to gain insight into shared mechanisms of tumor progression across species. Similar to human retinoblastoma, mouse tumors have low rates of single nucleotide variations. However, mouse retinoblastomas have higher rates of aneuploidy and regional and focal copy number changes that vary depending on the genetic lesions that initiate tumorigenesis in the developing murine retina. Furthermore, the epigenetic landscape in mouse retinoblastoma was significantly different from human tumors and some pathways that are candidates for molecular targeted therapy for human retinoblastoma such as SYK or MCL1 are not deregulated in GEMMs. Takentogether, these data suggest there are important differences between mouse and human retinoblastomas with respect to the mechanism of tumor progression and those differences can have significant implications for translational research to test the efficacy of novel therapies for this devastating childhood cancer.

Verification that cell lines used for cancer research are derived from malignantcells in primary tumors is imperative to avoid invalidation of study results. Retinoblastoma is a childhood ocular tumor that develops from loss of functionalretinoblastoma protein (pRb) as a result of genetic or epigenetic changes that affect both alleles of the RB1 gene. These patients contain unique identifiable genetic signatures specifically present in malignant cells. Primary cultures derived from retinoblastoma tumors can be established as non-adherent tumorspheres when grown in defined media or as attached monolayers when grown inserum-containing media. While the RB1 genotypes of tumorspheres match those of the primary tumor, adherent cultures have the germline RB1 genotype. tumorspheres derived from pRb-negative tumors do not express pRb and express the neuroendocrine tumor markers synaptophysin and microtubule-associated protein 2 (MAP2). Adherent cells are synaptophysin-negative and express pRb, the epithelial cell marker cytokeratin that is expressed in the retinal pigmented epithelium and the vascular endothelial cell marker CD34. While tumorspheres are of malignant origin, our results cast doubt on the assumption that adherent tumor-derived cultures are always valid in vitro models of malignant cells and emphasize the need for validation of primary tumor cultures.

Retinoblastoma (RB) is the most common intraocular cancer of infancy and childhood. This cancer is initiated by mutation on RB1, the tumor suppressor gene that is responsible for the regulation of both cell cycle and gnome stability inretinal cells. Patients with a constitutional mutation on RB1 can be inherited. RB occurs approximately 1 in every 15 000-20 000 live births. The worldwide mortality for this cancer is about 5%-11%. However, this rate rises to about 40%-70% in developing countries due to a delay in diagnosis. A wide variety of options are available for the treatment, but often a combination of therapies isadopted to optimize individualized care.

A survey of cancer in 159 3-year survivors of childhood soft tissue sarcoma and their relatives revealed a cancer excess in first-degree relatives primarily dueto cancers occurring before the age of 35 years and a highly significant excess in relatives of patients with second malignant neoplasms. tumors of soft tissue and bone, breast, and brain were in excess in relatives and as second malignant neoplasms in patients. To determine the most likely explanation for the observedcancer distribution, we applied segregation analysis under a unified version of the mixed model. The observed data were most compatible with a rare autosomal dominant gene with high penetrance (gene carriers had a 50% probability of cancer by age 30, increasing to 90% by age 60) as compared with a chance occurrence or a multifactorial explanation. We contrasted the relative odds of observing each pedigree under a sporadic, multifactorial, or major gene model, and identified 11 pedigrees in which familial clustering of cancer was significant, with the distribution of cancer strongly favoring a major gene in 9 pedigrees. The tumorsin these kindreds have been associated with alterations in specific genetic lociby tumor-specific genetic analysis. In particular, we observed soft tissue sarcoma, osteosarcoma and premenopausal ductal breast carcinoma tumors, perhaps attributable to loss of the Rb-1 suppressor gene on chromosome 13q, in the same patients and families. Study of the cancer predisposition segregating in 10 families by genetic linkage with markers of chromosome 13q and the Rb-1 gene have to date given negative LOD scores at 0 = 0 of Z = -1.2 to -13.0.(ABSTRACT TRUNCATED AT 250 WORDS)

The analysis of the molecular mechanisms governing multistep carcinogenesis became experimentally approachable since the identification and characterizationin tumor cells of altered or activated versions of cellular genes (oncogenes) that normally control cell growth and differentiation. The activating mutations confer new properties to the oncogene products and should therefore be considered as gain of function mutations. In addition, the oncogenes appear to act as dominant genetic traits since they act also in the presence of the homologous wild-type allele. However, the concept of a dominance of the transformed phenotype has been challenged by early experiments with somatic cell hybrids which showed that the fusion of normal and malignant cells may suppress the tumorigenic phenotype. The suppression or reversion of the malignant phenotype by the introduction of a normal chromosome into a tumor cell line has lent support to the idea that a family of cellular genes are coding for factors capable to interact with the cell-growth control machinery. These genes seem to reconstitute the normal control of cell growth even in the presence of an activated oncogene.In addition, a two-mutation model has been proposed to explain the epidemiological and clinical features of childhood cancers. According to the model, the development of these malignancies can be caused by the loss or inactivation of both alleles of cellular genes, as suggested by the somatic cellhybrid experiments where the function of the inactivated genes is restored by the contribution of those derived from the normal parental cells. This family of genes is designated as onco-suppressor genes since their product is necessary for the normal regulated cell growth and is lacking or inactivated in malignant cells. At gene level they should be considered as recessive genetic traits, since the tumor phenotype appears when both alleles of an onco-suppressor gene are inactivated. The mutations affecting their normal functions belong to the type "loss of function". The molecular analysis of retinoblastoma has led to the cloning and sequencing of the related onco-suppressor gene (RB gene) whose product displays the features of a gene-regulatory protein. In addition, a binding between the RB product and various viral onco-proteins (E1A, large T, E7) has been demonstrated, thus suggesting a mechanism of RB inactivation by which some DNA viruses can transform the host cell.(ABSTRACT TRUNCATED AT 400 WORDS)

The genetic predisposing factor for childhood retinoblastoma resides on the q14 band of human chromosome 13. However, a postulated second genetic event must take place for the disease to occur, which further research indicates involves inactivation of the remaining functional allele within 13q14. Our isolation of the gene within 13q14, called Rb, required creating a lambda-phage library that contained inserted fragments from human chromosome 13. One of the inserts, H3-8,detected a corresponding 1.8-kb HindIII fragment that was deleted in 2 of 37 retinoblastoma tumor DNAs. This suggested that the probed segment was linked to the Rb gene. A nearby probe, p7H30.7R, detected not only the human sequence but also a mouse homologue in a somatic cell hybrid carrying human chromosome 13. Weused the p7H30.7R probe for RNA analysis to detect any transcripts in a retinal cell line. The analysis showed a 4.7-kb transcript in the tumor cell line but not in several retinoblastomas. We also failed to detect a transcript in four retinoblastoma and two osteosarcoma samples using a corresponding cDNA fragment termed p4.7R. We used this probe to analyze the DNA from a large group of retinoblastomas and osteosarcomas and found gross changes in genomic structure in approximately 30% of the tumor DNAs. The boundaries of homozygously deleted fragments were mapped. In the analysis of an osteosarcoma and a retinoblastoma we discovered that the endpoints of the deletions were within the confines of the genetic unit defined by the probe. This indicated that the target of inactivation was the segment under study and not a neighboring DNA sequence.

The genetic predisposing factor for childhood retinoblastoma resides on the q14 band of human chromosome 13. However, a postulated second genetic event must take place for the disease to occur, which further research indicates involves inactivation of the remaining functional allele within 13q14. Our isolation of the gene within 13q14, called Rb, required creating a lambda-phage library that contained inserted fragments from human chromosome 13. One of the inserts, H3-8,detected a corresponding 1.8-kb HindIII fragment that was deleted in 2 of 37 retinoblastoma tumor DNAs. This suggested that the probed segment was linked to the Rb gene. A nearby probe, p7H30.7R, detected not only the human sequence but also a mouse homologue in a somatic cell hybrid carrying human chromosome 13. Weused the p7H30.7R probe for RNA analysis to detect any transcripts in a retinal cell line. The analysis showed a 4.7-kb transcript in the tumor cell line but not in several retinoblastomas. We also failed to detect a transcript in four retinoblastoma and two osteosarcoma samples using a corresponding cDNA fragment termed p4.7R. We used this probe to analyze the DNA from a large group of retinoblastomas and osteosarcomas and found gross changes in genomic structure in approximately 30% of the tumor DNAs. The boundaries of homozygously deleted fragments were mapped. In the analysis of an osteosarcoma and a retinoblastoma we discovered that the endpoints of the deletions were within the confines of the genetic unit defined by the probe. This indicated that the target of inactivation was the segment under study and not a neighboring DNA sequence.

Retinoblastoma (Rb) is an uncommon childhood tumor of the neural retina with a significant genetic component in its etiology. A small proportion of patients have a deletion in chromosome 13 encompassing band 13q14, an observation which permitted the assignment of the RB1 locus to this region. About 20% of Rb tumorsexhibit microscopic deletions of band 13q14 or monosomy 13. Trisomy 1q and i(6p)have also been reported in a high percentage of tumors. We analyzed the chromosome complements from direct preparations of 10 Rb tumors derived from seven patients. Modal chromosome numbers ranged from 45 to 48, and occasional duplications of the genomes were noted. In general, the tumors were chromosomally stable, although karyotypic evolution and random chromosome loss were encountered. Consistent abnormalities included trisomy 1q, i(6p), 6q-, and del(13)(q12----14). One patient with bilateral Rb had three tumor clones (two inone eye and one in the other) with chromosome abnormalities unrelated in origin.A second patient with unilateral Rb had two tumor clones with chromosome abnormalities again unrelated in origin. These two patients provide some of the first cytogenetic evidence for the multifocal origin of primary Rb. In the untreated tumor of a third patient, a homogeneously staining region (HSR) was detected in 1p32, indicating gene amplication in vivo; previously, an HSR at this site has been reported in the established Rb cell line Y79.#FAU - Chaum, E

Among the solid tumors of childhood and adolescence, osteosarcoma (OS) represents the most prominent example of efficient aggressive chemotherapy with secondary surgical therapy. A specific subclassification of the tumor is indispensable andmust include recent results of cell biology. The co-distribution of different collagen types I-VI reflects the diverse differentiation of osteosarcoma cells, supporting the concept of a pluripotent mesenchymal cell to be the stem cell of the tumor. In contrast, osteonectin (SPARC) may not be considered as a reliable marker for osteosarcoma. The experience of special proteins being secreted by osteosarcoma cells is rather limited. Detailed molecular biological studies are still lacking. A loss of alleles on chromosome 17, particularly in the defined region 17p 13, can be observed in more than 75% of ALL OS, suggesting the contribution of a tumor suppressor gene, p53, located in that region. It is a 53kd nucleophosphoprotein binding the major transforming protein, the large T antigen of Simian Virus 40. Immunohistological results showed positive staining with the antibody Pab 240 in 13 of 18 cases. In one osteoblastic OS, a novel splice mutation resulting in a fusing of exon 5 directly to exon 7 was detected.RB1 gene is also of major importance for the tumorigenesis of OS. The multidrug resistance (mdr) is associated with a membrane-bound channel-forming transport protein, the P-glycoprotein. It is a conserved plasma membrane component of about 170 kd. Both the human isoforms mdr 1 and mdr 3 are localised in the long arm ofchromosome 7.(ABSTRACT TRUNCATED AT 250 WORDS)

The retinoblastoma is a rare childhood tumor which occurs in children, 40% of them being diagnosed in an hereditary context. The gene involved in the hereditary predisposition and in the tumoral development was isolated (RB-1) andis of the antioncogene-type. RB-1 mutations were found in many other tumors. Theabsence of the antioncogene protein expression is responsible for the tumor development and a contrario its presence in normal cells has tumor suppressive properties. This property was demonstrated by phenotype reversion of retinoblastoma or other cell lines (with no RB-1 protein), induced by reintroduction of the gene coding for the normal RB-1 protein. The normal RB-1 protein undergoes multiple phosphorylations during the cell cycle, regulating its activity, the active form being hypophosphorylated. RB-1 is involved in the transcription regulation of many cell cycle genes, and in cell differentiation. Experimental animal models are under investigation, in order to established whether RB-1 overexpression in normal cells will protect them from tumor development, and to plan tumor gene therapy by injection of recombinant viruses allowing RB-1 expression in tumor cells.

Oncogenes are genes associated with causation of cancer. They were originally associated with the ability of retroviruses to cause tumors in animals. These viral oncogenes (V-onc) have their cellular counterparts (C-onc) called Proto oncogenes. Function of Proto oncogenes is to maintain cellular growth and development. Activation of these proto-oncogenes can occur due to mutation whichleads to uncontrolled cell growth. The Proto oncogenes can be grouped into different categories based on their protein products, i.e. protein kinases, growth factors, growth factor receptors, and DNA binding proteins. There are also genes that normally suppress malignant transformation and these are called anti oncogenes. Loss of their suppressor activity leads to unimpeded growth. Oncogeneabnormalities are seen in pediatric leukemias, lymphomas, and various solid tumors. Anti oncogenes are associated with retinoblastoma (Rb gene), Wilms' tumor, rhabdomyosarcoma and neuroblastoma, etc. Identification of these abnormalities have diagnostic, prognostic and therapeutic implications. The utility of oncogenes in classification of human cancer and monitoring cancer therapy is quite clear, but the future of these for therapeutic interventions remains uncertain. Role of c-abl oncogene in chronic myeloid leukemia (CML), bcl-2, in lymphomas, N-myc in neuroblastomas and retinoblastoma (Rb) gene in retinoblastomas is well understood and used in designing proper therapeutic approaches. Since oncogenes also control normal cellular function, their use fortherapy may be limited by the amount of damage to normal cells. Their maximum therapeutic benefit may be realized only when used in combination with other modalities.

BACKGROUND: children diagnosed with retinoblastoma, a rare cancer of the eye, tend to develop and die of second primary cancers in childhood and adolescence, but few investigations have followed patients into adulthood. Retinoblastoma is frequently caused by inherited mutations of the RB1 tumor suppressor gene. Most patients with germline (hereditary) mutations have bilateral disease. PURPOSE: We sought to quantify the mortality from second malignancies among long-term survivors of retinoblastoma and to identify factors that predispose to these deaths. METHODS: A retrospective cohort study examined mortality among 1603 patients enrolled at 1 year after diagnosis of retinoblastoma during the period 1914-1984. Data on demography, family history, and retinoblastoma treatment werecollected by medical chart review and questionnaire interview. Number of deaths,by cause, was compared with the corresponding expected figure based on U.S. mortality data for the general population for 1925-1990. RESULTS: Follow-up was complete for 1458 patients (91%) for a median of 17 years after retinoblastoma diagnosis. A total of 305 deaths occurred, 167 of them from retinoblastoma. There were 96 deaths from second primary tumors (relative risk [RR] = 30), 21 from other known causes (RR = 1.0), and 21 from ill-defined or unknown causes. Statistically significant excess mortality was found for second primary cancers of bone, connective tissue, and malignant melanoma and benign and malignant neoplasms of brain and meninges. Among 919 children with bilateral retinoblastoma, 90 deaths from second primary tumors occurred (RR = 60). Deaths from second tumors were more frequent among females (RR = 39) than males (RR = 22) (P = .007). The cumulative probability of death from second primary neoplasms was 26% at 40 years after bilateral retinoblastoma diagnosis, and additional cancer deaths occurred thereafter. Radiotherapy for retinoblastoma further increased the risk of mortality from second neoplasms. An excess of mortality from a second cancer, not seen in prior studies, was found among the 684 children with unilateral disease (RR = 3.1; 95% confidence interval = 1.0-7.3). CONCLUSIONS: These findings implicate germinal mutations in the retinoblastoma gene in second cancer mortality. Radiotherapy treatment for retinoblastoma appears to further enhance the inborn susceptibility to development of a second cancer. IMPLICATIONS: Patients with retinoblastoma, particularly bilateral retinoblastoma, should have careful follow-up, and interventions should be developed to reduce mortality from a second cancer.

BACKGROUND: Alveolar and embryonal rhabdomyosarcomas are soft-tissue tumors thatoccur mainly in childhood. The more aggressive alveolar subtype has been found to possess a characteristic chromosomal abnormality located near the retinoblastomasusceptibility gene (RB1). RB1 is a tumor suppressor gene implicated in the development of retinoblastoma and other, unrelated malignancies, especially osteogenic sarcomas and other second malignancies in retinoblastoma survivors. PURPOSE: The goals of our study were (a) to determine whether abnormalities of RB1 occur routinely in sporadic rhabdomyosarcomas, as reported for other sporadic malignancies, especially bone and soft-tissue sarcomas of adulthood; and (b) to assess differences in the functional status of the gene in embryonal and alveolar rhabdomyosarcomas that might explain the differing clinical aggressiveness of these two variants. METHODS: Analyses of messenger RNA (mRNA) and protein expression and immunohistochemical studies were performed on 11 rhabdomyosarcomacell lines from patients with no family history of retinoblastoma, and RB1 protein expression was studied by immunoprecipitation in primary tumor biopsy tissue from 18 patients with sporadic rhabdomyosarcoma (five embryonal and 13 alveolar). RESULTS: The RB1 gene appears to be normal in structure, expression, and function and is comparably phosphorylated in both forms of childhood rhabdomyosarcoma. Normal-size RB1 mRNA was present in ALL rhabdomyosarcomas, whereas clearly abnormal expression was documented in the controls, as expected:mRNA transcripts were truncated in Y79 retinoblastoma and absent in DU4475 breast carcinoma. In addition, immunoprecipitation with antibody to RB1 protein indicated the presence of normal RB1 protein in ALL rhabdomyosarcomas. CONCLUSIONS: These findings are distinct from those for other adult asarcomas, in which RB1 expression frequently is reported as abnormal. They are particularly surprising in view of the high incidence of RB1 abnormalities in osteosarcoma, the bone tumor most associated with retinoblastoma. The etiology and biologic behavior of rhabdomyosarcoma are, thus, unlikely to be dependent on RB1 mutations. IMPLICATIONS: The findings reported here clearly imply that the RB1 gene is structurally and functionally normal in childhood rhabdomyosarcoma. Other, as yet unidentified, genetic defects are apparently etiologic in this particular sarcoma.

Two different processes appear to be involved in the initiation of hepatocarcinogenesis by chronic hepatitis B virus (HBV) infection and by chronichepatitis C virus (HCV) infection. Initiation of hepatocellular carcinoma (HCC) by chronic HBV infection usually occurs early in life; most patients have had onset of HBV infection before the end of childhood, although rare cases of HCC have been reported following HBV infections acquired in adulthood. In contrast, HCV-associated HCC in many cases probably develops after a chronic HCV infectionthat was acquired during adulthood. HBV-DNA usually is integrated in the tumor DNA of HBV-associated HCC; it produces two proteins that can transactivate knownoncogenes in vitro and that theoretically could affect genes at distant sites invivo. HCV is a nonintegrating virus and no transactivating HCV proteins have been identified so far. In the later stages of hepatocarcinogenesis, "tumor promotion" and "tumor progression," HBV-associated HCC may share certain features with those of HCV-associated HCC. Chronic inflammation and cirrhosis, accompanied by regenerative processes, may function as a tumor promoter, providing a common pathway from chronic HBV or HCV infection to HCC. tumor progression may be brought about in HCC by mutations of the p53 tumor suppressor gene. mutations ofthis gene are common in HCCs, and they are found more often in advanced human HCCs than in small, well-differentiated HCCs. The prevalences of p53 mutations are similar in HBV-associated and HCV-associated HCCs (30-50%). Even in the absence of a p53 mutation, the functions of normal p53 can be inactivated as a result of binding by viral or by cellular proteins. It is not known yet whether this type of binding contributes to the development of HCC, but p53 binding by the HBV X protein in vitro has been reported. Abnormalities of the RB tumor suppressor gene also have been found frequently in HCC patients, particularly inHCCs that contain p53 mutations.

The 'two-hit' hypothesis for the development of the childhood eye cancer, retinoblastoma (Rb), predicts that bilaterally affected individuals will carry germline mutations. The second suggestion is that patients with early presentation of unilateral tumours also carry predisposing mutations. We have used SSCP analysis to study the 27 individual exons of the RB1 gene in constitutional DNA from 3 patients whose tumours were treated under the age of 12 months. Bandshifts on SSCP gels were detected in 2 of these patients which, on sequencing, were shown to be a C-->T transition converting a CGAarg to a TGAstopcodon in exon 17 and an 8 bp deletion in exon 20 resulting in a downstream stop codon. The mutations seen in these patients are reminiscent of those seen in patients with hereditary Rb and confirms that at least some early onset unilateral cases carry constitutional mutations, which has important implications for genetic screening and counselling of these individuals.

The etiopathogenesis of neoplastic diseases is characterized by its multiple nature. Multiple biological and physical agents have been identified as initiating or promoting neoplastic mechanisms. However, they ALL appear to have common molecular basis, granting genetic instability and causing somatic derangements to preneoplastic and tumor cells. Target genes implicated in cellular transformation and tumor progression have been divided into two categories: proto-oncogenes (that when activated become dominant events characterized by gain of function) and tumor suppressor genes (recessive events characterized by the loss of function). Alteration in proto-oncogenes and tumor suppressor genes seem equally prevalent among human cancers. Multiple mutations appear to be required to conform the malignant phenotype. It is, therefore, conceivable to view cancer as fundamentally a genetic disease entailing inherited (also called "germline") or acquired (also termed "somatic") mutations of genes in these two categories. The concept of tumor suppressor genes was established in studies with somatic cell hybrids, revealing that when malignant cells were fused with normal cells some of the hybrids were nontumorigenic. Clinically, the existence and relevance of this category of genes was based on epidemiological studies of the intraocular childhood tumor retinoblastoma, and it was postulatedthat two independent events were needed to inactivate a given gene. It was further shown that, in general, that was achieved by an allelic loss followed bya point mutation of the remaining allele. A family of genes has been characterized that follows this "two-hit" model including the two prototype suppressors genes: the retinoblastoma (RB) and the TP53 (also known as p53) genes. These genes encode a variety of molecules with distinct biological properties, including cell cycle regulation and cellular differentiation. Germline and somatic mutations of these genes appear to be the most common abnormalities found in human cancer including bladder neoplasms. More recent studies have shown that inactivation of some of these genes (i.e., TP53) occurs in bladder tumors that have a more aggressive clinical outcome and poor prognosis. In the following subheadings, the authors have reviewed the molecularabnormalities associated with these recessive genes in bladder tumors and discuss the potential clinical use of their detection. The implementation of objective predictive assays to identify these alterations in clinical material will enhance the ability to assess tumor biological activities and to design effective treatment regimens. The need now is to translate this newly developed scientificknowledge into diagnostic and therapeutic strategies, which, in turn, will enhance quality of life and prolong patient survival.

In this report we review current studies concerning the RB-1 gene expression in acute leukemias. The RB-1 gene was analyzed in several studies by protein-, RNA and DNA-techniques in acute lymphoblastic leukemia (ALL) as well as in acute myelogenous leukemia (AML). The frequency of RB-1 inactivation in ALL-patients ranged between 30% and 64% in several studies. Structural abnormalities of the RB-1 gene were reported in 18% of ALL-patients and in 27% of Philadelphia chromosome-positive ALL, respectively. The proportion of AML-patients with absent RB-1 protein expression ranged between 19% and 55%. Structural RB-1-abnormalities in AML were predominantly reported in leukemias with monocytic differentiation. Furthermore, the prognostic value of an abnormal RB-1 gene expression was also estimated in some studies. In childhood ALL RB-1 inactivation was reported to have prognostic significance while in contrast, in another study on adults no prognostic value of RB-1 was found. In 4 out of 5 documented studies AML-patients with RB-1 inactivation generally had a poorer prognosis. In conclusion, RB-1 inactivation is frequently observed in acute leukemia. The prognostic value of low RB-1 expression is controversial but the majority of published studies foundlow RB-1 expression to be a negative prognostic predictor, in acute leukemia.

Retinoblastoma is a childhood malignancy of the eye. Almost ALL patients with familial or bilateral disease suffer from the hereditary form of the disease that is caused by germline mutations in one allele of the RB1 gene. tumor developmentis initiated by the loss of the second RB allele in a retinal progenitor cell. Most patients with isolated unilateral disease have nonhereditary retinoblastomaand thus do not carry a mutant allele in their germline. In no patient, the presence of a germline mutation can be excluded clinically. Consequently, relatives are at an increased risk for retinoblastoma. Molecular testing, however, enables accurate risk prediction provided that samples are available. In some relatives an increased risk can be excluded by segregation analysis. Most often, however, identification of the disease causing mutation is necessary for accurate risk prediction. mutation analysis, which is impeded by the size and complexity of the RB gene, is facilitated by use of efficient screening methods.Using these methods, the oncogenic mutation can be identified in most patients. Therefore, predictive testing has become an integral part of contemporary management of retinoblastoma.

PURPOSE: Forty percent of cases of retinoblastoma, a childhood malignancy of theretina, are linked to the inheritance of a mutant allele of the retinoblastoma susceptibility gene Rb1. tumor penetrance varies among carriers in different family pedigrees, indicating that other genetic factors may modify risk for occurrence of retinoblastoma. This study was undertaken to determine whether multiple genetic loci modify the risk for retinoblastoma in mice. METHODS: A line of alphaAcry-HPV16E6/E7 transgenic mice expressing the human papillomavirus type16 E6 and E7 oncogenes (HPV-16 E6 and E7) ectopically in the retina was characterized. E6 and E7 proteins bind to and inactivate the cellular tumor suppressor proteins p53 and Rb, respectively. RESULTS: Retinoblastomas developedrarely when the alphaAcry-HPV16E6/E7 transgene was maintained on the FVB background, but tumors arose with high frequency on C57BL/6 X FVB and C3H x FVB F1 hybrid backgrounds. The incidence of retinoblastoma in the LHbeta-TAG transgenic mice, which express simian virus 40 large tumor antigen (SV40 T-ag), was also influenced by the FVB and C57BL/6 backgrounds. Resistance of the alphaAcry-HPV16E6/E7 FVB mice to retinoblastoma mapped in part to the retinal degeneration (rd) locus. However, multiple genetic experiments indicate that resistance to retinoblastoma depends on additional loci in FVB mice. CONCLUSIONS: Multiple cellular genes can modify risk for retinoblastoma in mice.