4297

MLL

ALL-1|CXXC7|HRX|HTRX1|KMT2A|MLL/GAS7|MLL1A|TET1-MLL|TRX1;myeloid/lymphoid or mixed-lineage leukemia (trithorax homolog, Drosophila);MLL;myeloid/lymphoid or mixed-lineage leukemia (trithorax homolog, Drosophila)

CDK6/MLL fusion protein|CXXC-type zinc finger protein 7|MLL-AF4 der(11) fusion protein|MLL/GAS7 fusion protein|MLL/GMPS fusion protein|histone-lysine N-methyltransferase MLL|lysine N-methyltransferase 2A|trithorax-like protein|zinc finger protein HRX

11q23

protein-coding

Rearrangements and fusion of the MLL gene with various alternative partner genesoccur in approximately 80% of infant leukemias and are acquired during fetal hemopoiesis in utero. Similar MLL gene recombinants also occur in topoisomerase II-inhibiting drug-induced leukemias. These data have led to the suggestion thatsome infant leukemia may arise via transplacental fetal exposures during pregnancy to substances that form cleavable complexes with topoisomerase II and induce illegitimate recombination of the MLL gene. A structural feature shared by many topoisomerase II-inhibiting drugs and other chemicals is the quinone moiety. We assayed, by PCR-RFLP, for a polymorphism in an enzyme that detoxifies quinones, NAD(P)H:quinone oxidoreductase (NQO1), in a series (n = 36) of infant leukemias with MLL rearrangements versus unselected cord blood controls (n = 100). MLL-rearranged leukemias were more likely to have genotypes with low NQO1 function (heterozygous CT or homozygous TT at nucleotide 609) than controls (odds ratio, 2.5; P = 0.015). In contrast, no significant allele bias was seen in other groups of pediatric leukemias with TEL-AML1 fusions (n = 50) or hyperdiploidy (n= 29). In the subset of infant leukemias that had MLL-AF4 fusion genes (n = 21),the bias increase in low or null function NQO1 genotypes was more pronounced (odds ratio, 8.12; P = 0.00013). These data support the idea of a novel causal mechanism in infant leukemia involving genotoxic exposure in utero and modulation of impact on a selective target gene by an inherited allele encoding a rate-limiting step in a carcinogen detoxification pathway.

Acute lymphoblastic leukemia (ALL) is the most common cancer in children and is among the most curable of the pediatric malignancies. Many clinical, biological,genetic, and molecular features have been identified as having prognostic significance in the outcome of patients with ALL. The standard features are age and WBC at diagnosis, with infants (less than one year), adolescents (greater than nine years), and children with WBC above 50,000/microl being at higher risk. Certain chromosomal abnormalities are also strong predictors; in particular, thePhiladelphia chromosome and MLL gene rearrangements (especially in infants) are adverse features, while TEL-AML1 is favorable. It is important to note, however,that even the most important known predictors explain only a small proportion ofthe variability in outcome. These features are currently used to tailor the intensity of treatment so that the toxicity of treatment can be minimized and cure rates can continue to improve. This article reviews time-honored prognosticfeatures, recent advances, and future directions in this field.

Acute leukemia is the most common form of childhood cancer and is the primary cause of cancer-related mortality in children. In the United approximately 3250 cases are diagnosed annually in children and adolescents younger than 20 years, of whom 2400 have acute lymphoblastic leukemia (ALL). Treatment results in childhood ALL continue to improve, and the expected current cure rates approach 75 to 80% of ALL children with ALL, including T-ALL and mature B-cell ALL, the two variants that, not too long ago, had a considerably poorer prognosis compared with the common form of BpALL. The most significant new development in the past 2 years has been the development of further evidence for fetal origin of childhoodleukemias, and additional evidence to support the notion that postnatal events modulating the events of immune-mediated elimination of these leukemic clones play a major role in the eventual development of clinical disease. Other epidemiologic developments include (1) increased appreciation of the role of drug-metabolizing enzymes, both in determining the predisposition to leukemia and response to therapy; and (2) both clinical observations and gene expression studies seeming to identify a new approach to the evaluation and treatment of children with MLL (11q23) rearrangements. A most remarkable new development in the induction therapy of childhood leukemia and lymphoma in the United States isthe use of urate oxidase for prevention of tumor lysis syndrome and the associated uric acid nephropathy. Drug resistance, determined either on leukemicblast cells in vitro or by studies of MRD, is being looked at critically in an effort to improve the treatment results further. Consolidation with HDMTX has gained wider popularity with the realization that effective CNS prophylaxis can be achieved with intrathecal therapy plus HDMTX for consolidation. In contrast to ALL, the progress in the therapy of acute myeloid leukemia (AML) lags behind, with cure rates of approximately 40 to 50%. There is no convincing evidence for substitution of daunorubicin with other anthracyclines, nor evidence for using high-dose cytarabine during induction in childhood AML. Rather, a 3 + 10 regimenwith total daunorubicin 180 mg/m2 and cytarabine 100 to 200 mg/2 for 10 days appears to yield the best results. The most important component of the postremission chemotherapy continues to be several courses of high-dose cytarabine. The results from the MRC 10, LAME 89/91 studies and the recent BFM 93 trial with high-dose cytarabine and mitoxantrone suggest that there may be some benefit to including this combination in the postremission phase of AML. Despitethese improvements in chemotherapy, allogeneic BMT from a matched family donor remains the best option for most patients (excluding Down syndrome, APL, and possibly those with inv16). Newer prognostic markers of interest include FLT3/ITD and minimal residual disease at the end of induction therapy.

Acute leukemia is the most common form of childhood cancer and is the primary cause of cancer-related mortality in children. In the United approximately 3250 cases are diagnosed annually in children and adolescents younger than 20 years, of whom 2400 have acute lymphoblastic leukemia (ALL). Treatment results in childhood ALL continue to improve, and the expected current cure rates approach 75 to 80% of ALL children with ALL, including T-ALL and mature B-cell ALL, the two variants that, not too long ago, had a considerably poorer prognosis compared with the common form of BpALL. The most significant new development in the past 2 years has been the development of further evidence for fetal origin of childhoodleukemias, and additional evidence to support the notion that postnatal events modulating the events of immune-mediated elimination of these leukemic clones play a major role in the eventual development of clinical disease. Other epidemiologic developments include (1) increased appreciation of the role of drug-metabolizing enzymes, both in determining the predisposition to leukemia and response to therapy; and (2) both clinical observations and gene expression studies seeming to identify a new approach to the evaluation and treatment of children with MLL (11q23) rearrangements. A most remarkable new development in the induction therapy of childhood leukemia and lymphoma in the United States isthe use of urate oxidase for prevention of tumor lysis syndrome and the associated uric acid nephropathy. Drug resistance, determined either on leukemicblast cells in vitro or by studies of MRD, is being looked at critically in an effort to improve the treatment results further. Consolidation with HDMTX has gained wider popularity with the realization that effective CNS prophylaxis can be achieved with intrathecal therapy plus HDMTX for consolidation. In contrast to ALL, the progress in the therapy of acute myeloid leukemia (AML) lags behind, with cure rates of approximately 40 to 50%. There is no convincing evidence for substitution of daunorubicin with other anthracyclines, nor evidence for using high-dose cytarabine during induction in childhood AML. Rather, a 3 + 10 regimenwith total daunorubicin 180 mg/m2 and cytarabine 100 to 200 mg/2 for 10 days appears to yield the best results. The most important component of the postremission chemotherapy continues to be several courses of high-dose cytarabine. The results from the MRC 10, LAME 89/91 studies and the recent BFM 93 trial with high-dose cytarabine and mitoxantrone suggest that there may be some benefit to including this combination in the postremission phase of AML. Despitethese improvements in chemotherapy, allogeneic BMT from a matched family donor remains the best option for most patients (excluding Down syndrome, APL, and possibly those with inv16). Newer prognostic markers of interest include FLT3/ITD and minimal residual disease at the end of induction therapy.

The outcome for children with acute lymphoblastic leukemia (ALL) has improved dramatically with current therapy resulting in an event free survival exceeding 75% for most patients. However significant challenges remain including developing better methods to predict which patients can be cured with less toxic treatment and which ones will benefit from augmented therapy. In addition, 25% of patientsfail therapy and novel treatments that are focused on undermining specifically the leukemic process are needed urgently. In Section I, Dr. Carroll reviews current approaches to risk classification and proposes a system that incorporates well-established clinical parameters, genetic lesions of the blast as well as early response parameters. He then provides an overview of emerging technologiesin genomics and proteomics and how they might lead to more rational, biologically based classification systems. In Section II, Drs. Mary Relling and Stella Daviesdescribe emerging findings that relate to host features that influence outcome, the role of inherited germline variation. They highlight technical breakthroughsin assessing germline differences among patients. Polymorphisms of drug metabolizing genes have been shown to influence toxicity and the best example isthe gene thiopurine methyltransferase (TPMT) a key enzyme in the metabolism of 6-mercaptopurine. Polymorphisms are associated with decreased activity that is also associated with increased toxicity. The role of polymorphisms in other genes whose products play an important role in drug metabolism as well as cytokine genes are discussed. In Sections III and IV, Drs. James Downing and Cheryl Willman review their findings using gene expression profiling to classify ALL. Both authors outline challenges in applying this methodology to analysis of clinical samples. Dr. Willman describes her laboratory's examination of infant leukemia and precursor B-ALL where unsupervised approaches have led to the identification of inherent biologic groups not predicted by conventional morphologic, immunophenotypic and cytogenetic variables. Dr. Downing describes his results from a pediatric ALL expression database using over 327 diagnostic samples, with 80% of the dataset consisting of samples from patients treated on a single institutional protocol. Seven distinct leukemia subtypes were identified representing known leukemia subtypes including: BCR-ABL, E2A-PBX1, TEL-AML1, rearrangements in the MLL gene, hyperdiploid karyotype (i.e., > 50 chromosomes),and T-ALL as well as a new leukemia subtype. A subset of genes have been identified whose expression appears to be predictive of outcome but independent verification is needed before this type of analysis can be integrated into treatment assignment. Chemotherapeutic agents kill cancer cells by activating apoptosis, or programmed cell death. In Section V, Dr. John Reed describes majorapoptotic pathways and the specific role of key proteins in this response. The expression level of some of these proteins, such as BCL2, BAX, and caspase 3, has been shown to be predictive of ultimate outcome in hematopoietic tumors. New therapeutic approaches that modulate the apoptotic pathway are now available andDr. Reed highlights those that may be applicable to the treatment of childhood ALL.

childhood cancer is rare comprising less than 1% of ALL malignancies diagnosed each year in developed countries. Leukaemia is the commonest form of cancer in children accounting for around a third of ALL childhood cancer, with acute lymphoblastic leukaemia (ALL) being the most prevalent. Biologically specific subtypes of ALL and acute myeloblastic leukaemia (AML), the other major morphological type of childhood leukaemia, are characterised by chromosomal changes. Whilst over 200 genes have been associated with chromosomal translocations, to date, only MLL, TEL, and AML1 have been linked with childhoodleukaemia. Interestingly, there is increasing evidence to support the theory that gene rearrangements such as these may originate in utero. As with many other human diseases, both genetic and environmental factors have been implicated in the aetiology of the disease. Although much has been documented with regard to diet, smoking, alcohol consumption and recreational and prescription drug use during pregnancy, there is no consistent evidence to support a link with any of these factors and childhood leukaemia. However, findings from studies investigating prenatal and early life exposures are often based on small numbersof cases as both the type of cancer and exposure are rare. Furthermore, accurateinformation relating to past exposures can be difficult to obtain and is often reliant on self-reporting. To further our understanding of the aetiology of childhood leukaemia and lymphoma, there are areas which clearly warrant investigation. These include collection of parental dietary folate data combinedwith genetic analysis of the folate related genes, in utero exposure to DNA topoisomerase II inhibitors, and the possible effects of assisted reproduction technology on disease susceptibility.

Leukemia is the most common childhood cancer and a major source of morbidity andmortality. The etiology of childhood leukemia remains largely unknown. Cytogenetic abnormalities determine disease subtypes, prognosis, clinical presentation, and course and may help in discovering etiological factors. Epidemiologic investigations of leukemia are complicated by many factors, including the rarity of the disease, necessitating careful study design. Two emerging areas of interest in leukemia etiology are birth weight and diet. High birth weight has been associated with increased risk of childhood leukemia. The biological mechanism behind this association may involve insulin-like growth factor I (IGF-I), which is associated with high birth weight. IGF-I may act by increasing the absolute number of stem cells available for transformation, stimulating the growth of cells that are already transformed, or a combination of effects. Diet has been linked with leukemia. Maternal dietary DNA topoisomerase II (DNAt2) inhibitor intake is associated with infant acute myeloid leukemia (AML) with the MLL gene translocation. Increased intake of fruits and vegetableshas been associated with decreased leukemia risk and, relatedly, lack of maternal folate supplementation has been associated with increased childhood leukemia risk, possibly by causing DNA hypomethylation and increased DNA strand breaks. Methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms modify this risk.

Primary genetic abnormalities of leukemia cells have important prognostic significance in childhood acute leukemia. In the last two years 30 newly diagnosed or recurrent childhood ALL bone marrow samples were analyzed for chromosomal abnormalities with conventional G-banding and interphase-fluorescence in situ hybridization (I-FISH) using probes to detect BCR/ABL fusions, cryptic TEL/AML1 and MLL rearrangements and p16(9p21) tumor suppressor gene deletions. G-banded karyotype analysis found clonal chromosomal aberrations in 50% of cases. With the use of complementary I-FISH techniques, ALL-specific structural and numerical changes could be identified in 70% of the patients. Nine cases (30%) had subtle chromosomal aberrations with prognostic importance that had not been detected in G-banded analysis. Conventional G-banding yielded additional information (rare and complex structural aberrations) in 19% of patients. The most common aberration (30%) was AML1 copy number increase present in G-banded hyperdiploid karyotype as a chromosome 21 tetrasomy in the majority of cases; one case displayed 5-6 copies and in another case amplification of AML1 gene on der(21) was combined with TEL/AML1 fusion of the homologue AML1 gene and deletion of the remaining TEL allele. High hiperdiploidy was detected in 6 cases, in one patient with normal G-banding karyotype. TEL/AML1 fusion signals were identifiedin four patients. Deletion of p16 locus was found in eight cases (23%), of whichonly two had cytogenetically visible rearrangements. G-banding in combination with I-FISH has produced major improvements in the sensitivity and accuracy of cytogenetic analysis of ALL patients and this method helps to achieve a more precise identification of different risk categories in order to choose the optimal treatment.

Mixed lineage leukemia is a very aggressive blood cancer that predominantly occurs in pediatric patients. In contrast to other types of childhood acute leukemias, mixed lineage leukemia presents with a dismal prognosis and despite the availability of advanced treatment methods cure rates have stagnated over the last years. Mixed lineage leukemia is characterized by the presence of MLL fusion proteins that are the result of chromosomal translocations affecting the MLL gene at 11q23. These events juxtapose the amino-terminus of the histone methyltransferase MLL with a variety of different fusion partners that destroy normal histone methyltransferase function of MLL and replace it by heterologous functions contributed by the fusion partner. The resulting chimeras are transcriptional regulators that take control of targets normally controlled by MLL with the clustered HOX homeobox genes as prominent examples. Recent studies suggested that MLL fusion partners activate transcription by two different mechanisms. Some of these proteins are themselves chromatin modifiers that introduce histone acetylation whereas other fusion partners can recruit histone methyltransferases. In particular, histone H3 specific methylation at lysine 79 catalyzed by DOT1L has been recognized as a hallmark of chromatin activated by MLL fusion proteins. Interestingly, several frequent MLL fusion partners seem tocoordinate DOT1L activity with a protein complex that stimulates the elongation phase of transcription by phosphorylating the carboxy-terminal repeat domain of RNA polymerase II. The discovery of these novel enzymatic activities that are essentially involved in MLL fusion protein function presents potential new targets for a rational drug development.

Treatment of children's acute lymphoblastic leukemia has been at the forefront of conventional chemotherapy development. Despite outstanding results in long-term survival of acute lymphoblastic leukemia, development of therapies for acute myeloid leukemia (AML) have lagged behind. AML in children demonstrate similar long-term survival compared with adults 18-65 years of age: 40-50% overall long-term survival. AML is a heterogeneous disease in both adults and children, but the presence of recurrent chromosome translocations and mutations in children are lower than in adult AML. In particular, patients without chromosome aberrancies have been examined for stratification through examination of gene expression. The paper from Baglobind and coauthors proposes a useful prognostication by gene-expression analysis of 75 gene pairs in 40% of patient cases, accurately discriminating mixed lineage leukemia (MLL) gene rearrangement, t(8;21)(q22;q22), inv(16)(p13q22), t(15;17)(q21;q22) and t(7;12)(q36;p13)-positive AML. Gene-expression analysis of AML has provided an important research tool for uncovering information about AML biology that can beused for the development of novel therapies.

BACKGROUND: miRNAs regulate gene expression, and thus play an important role in critical cellular processes. Aberrant miRNA expression patterns have been found in various types of cancer. So far, information about the expression of miRNAs in pediatric acute myeloid leukemia is limited. PROCEDURE: We studied expression ofmiR-29a, -155, -196a, and -196b by stem-loop based RT-qPCR in 82 pediatric acutemyeloid leukemia patients selected to represent relevant cytogenetic and molecular subgroups. RESULTS: High miR-196a and -b expression was observed in patients carrying MLL gene rearrangements (P < 0.001), NPM1 mutations (P < 0.001), or FLT3-ITD in a cytogenetically normal background (P ALL other patients. In contrast, CEBPA mutated cases had a low expression of miR-196a and -b (P expression of miR-196a and -b was correlated withexpression of neighboring HOXA and HOXB genes (Spearman's r = 0.46-0.82, P < 0.01). expression of miR-155 was not related to cytogenetic features but high expression of miR-155 was observed in FLT3-ITD (P = 0.001) and NPM1-mutated cases (P = 0.04). Lower miR-29a expression was mainly observed in MLL-rearranged pediatric acute myeloid leukemia, specifically in cases carrying t(10;11) (P < 0.001). CONCLUSIONS: We show aberrant expression of specific miRNAs in clinically relevant cytogenetic and molecular subgroups of pediatric acute myeloid leukemia, suggesting a role for these miRNAs in the underlying biology in these specific subgroups.#CI- Copyright (c) 2011 Wiley Periodicals, Inc.

Early infancy (< 1 year of age), massive tumor cell burden, and extremely poor prognosis are characteristic features of a particular subset of childhood acute leukemias (AL). In these cases, chromosome aberrations at the 11q23 band are themost frequently reported cytogenetic abnormalities. We have recently cloned a genetic locus named ALL-1, in which DNA breakpoints are clustered in leukemic patients with 11q23 aberrations. Analysis of the ALL-1 genomic configuration in DNA from 15 infants with AL showed specific ALL-1 rearrangements in 12 cases (80%), including 5 with normal karyotypes. These findings indicate that a consistent genetic defect underlies this particular leukemic subset.

Nearly 80 percent of infant leukemias present with an abnormality involving the MLL gene at 11q23. Moreover, secondary acute myeloid leukemias (AML) that occur as the result of chemotherapy agents, which are known to inhibit DNA topoisomerase II, often manifest the same MLL abnormalities. It has been hypothesized that de novo infant leukemias may occur as a result of maternal exposure to agents in diet and medications that inhibit DNA topoisomerase II. Three epidemiologic studies of childhood leukemia with similar methodologies were conducted in the United States and Canada over the past 10 years by the children's cancer Group (CCG). Of the total 771 mothers of infants diagnosed at one year of age or less (< 12.5 months) who originally were interviewed (303 infant cases and 468 matched controls) across the three studies, follow-up questionnaire data on maternal exposure to potential DNA topoisomerase II inhibitors during pregnancy were available on 84 cases and 97 matched controls in the US. For maternal diet, a composite variable was created that consisted of 10foods identified alpha priori as containing DNA topoisomerase II inhibitors. There were no significant trends with increasing maternal consumption for eitherthe overall group, or the acute lymphoblastic leukemia (ALL) stratum. However, within the AML stratum, there was a statistically significant positive association (P trend = 0.04) with increasing consumption of DNA topoisomerase II-inhibitor containing foods (odds ratio [OR] = 9.8, 95 percent confidence interval [CI] = 1.1-84.8; OR = 10.2, CI = 1.1-96.4; for medium and high consumption, respectively). Other potential topoisomerase II inhibitors were explored; no significant findings were found. Results of this preliminary study,in combination with molecular data, should be used in future investigations of childhood leukemia (particularly, infant) to justify the incorporation of a detailed dietary history.

To study prognostic factors in infant acute myeloid leukemia (AML), we analyzed 44 children treated on childrens cancer Group protocols for MLL gene rearrangement by Southern blot, cytogenetic 11q23 abnormalities, and reactivity with monoclonal antibody 7.1. This antibody detects the human homologue of the rat NG2 chondroitin sulfate proteoglycan molecule, which has previously been reported to be expressed on human melanoma. NG2 has been found to be expressed on human leukemic blasts but not on other hematopoietic cells. In childhood AML, NG2 cell surface expression correlated with poor outcome and with some but not ALL 11q23 rearrangements. In childhood acute lymphoblastic leukemia, NG2 expression correlated with poor outcome and with balanced 11q23 translocations. In this study, 29 of 44 (66%) of infants with AML showed MLL rearrangement and, as expected, this group had a high incidence of French-American-British M4/M5 morphology (22/29). Of the cases tested, 35.1% (13/37) were NG2 positive. ALL (13/13) NG2-positive cases were rearranged at MLL, whereas only 46% (11/24) of NG2-negative cases had MLL rearrangement. NG2 expression did not correlate with poor outcome (P = .31); there was a trend towards a worse outcome with MLL rearrangement (P = .13). Thus monoclonal antibody 7.1 does not detect ALL cases of MLL rearrangement in infant AML.

Advances in the molecular characterization of leukemic cells have greatly improved the precision of diagnosis and treatment assignment as well as the monitoring of residual disease in both acute lymphoblastic leukemia and acute myeloid leukemia. Currently, specific genetic rearrangements can be identified in as many as 50% of children with either acute lymphoblastic leukemia or acute myeloid leukemia. The genes p16 (or MTS1) and TEL/AML1 are now respectively recognized as the most common tumor suppressor and fusion genes in childhood acute lymphoblastic leukemia. Increasingly, contemporary protocols for the acuteleukemias are relying on genetic information to guide treatment decisions. Examples include the use of allogeneic hematopoietic stem cell transplantation for acute lymphoblastic leukemia with the BCR-ABL fusion gene or MLL rearrangement, and for acute myeloid leukemia with monosomy 7; antimetabolite-based therapy for acute lymphoblastic leukemia cases with hyperdiploidy of more than 50 chromosomes (DNA index > or = 1.16); and retinoic acid and anthracycline-containing regimens for the acute promyelocytic acute myeloid leukemia subtype with PML-RARA fusion. Other efforts are being made to reduce the long-term sequelae of treatment. Indeed, extended intrathecal therapyand intensive systemic chemotherapy will, in ALL likelihood, replace cranial irradiation as subclinical central nervous system therapy for patients with intermediate-risk acute lymphoblastic leukemia, and perhaps even for those with high-risk acute lymphoblastic leukemia. The challenge now is to identify specific treatments for other genetically defined subtypes of leukemia. This goal will berealized only through protocol-based studies employing uniform criteria for defining risk status.

Segmental jumping translocations are chromosomal abnormalities in treatment-related leukemias characterized by multiple copies of the ABL and/or MLL oncogenes dispersed throughout the genome and extrachromosomally. Because gene amplification potential accompanies loss of wild-type p53, we examined the p53 gene in a case of treatment-related acute myeloid leukemia (t-AML) with MLL segmental jumping translocation. The child was diagnosed with ganglioneuroma andembryonal rhabdomyosarcoma (ERMS) at 2 years of age. Therapy for ERMS included alkylating agents, DNA topoisomerase I and DNA topoisomerase II inhibitors, and local radiation. t-AML was diagnosed at 4 years of age. The complex karyotype ofthe t-AML showed structural and numerical abnormalities. Fluorescence in situ hybridization analysis showed multiple copies of the MLL gene, consistent with segmental jumping translocation. A genomic region including CD3, MLL, and a segment of band 11q24 was unrearranged and amplified by Southern blot analysis. There was no family history of a cancer predisposing syndrome, but single-strandconformation polymorphism (SSCP) analysis detected identical band shifts in the leukemia, ganglioneuroma, ERMS, and normal tissues, consistent with a germline p53 mutation, and there was loss of heterozygosity in the ERMS and the t-AML. Sequencing showed a CGA-->TGA nonsense mutation at codon 306 in exon 8. The results of this analysis indicate that loss of wild-type p53 may be associated with genomic instability after DNA-damaging chemotherapy and radiation, manifestas a complex karyotype and gene amplification in some cases of t-AML.

Leukemia in the first year of life is extremely rare world-wide. However, unlikeleukemias in older children, nearly 75% of infant leukemias demonstrate a specific abnormality involving a gene, MLL, on chromosome band 11q23. Molecular studies suggest strongly that these leukemias occur in utero. Treatment-related acute myeloid leukemias (AML), associated with specific chemotherapeutic agents that inhibit DNA topoisomerase II (topo 2), also manifest identical abnormalities involving the MLL gene. This led us to speculate that maternal exposure during pregnancy to environmental agents that inhibit DNA topo 2 may be associated withthe development of leukemia in infants. DNA topo 2 inhibitors have been found inspecific fruits and vegetables, and in soy, coffee, wine, tea and cocoa, as wellas in certain pesticides, solvents and medications. In a preliminary study, we reinterviewed mothers of infant cases and their matched controls who had participated previously in 1 of 3 epidemiologic studies of childhood leukemia conducted by the children's cancer Group over a 10-year period. We evaluated potential DNA topo 2 inhibitor exposure through maternal diet and medications. Of the 84 original matched sets who were reinterviewed, there was no positive association with increasing maternal consumption of DNA topo 2 inhibitor-containing foods either for the overall group or for infants in the acute lymphoblastic leukemia stratum. However, there was an approximately 10-fold higher risk of infant AML with increasing maternal consumption of DNA topo 2 inhibitor-containing foods. The assay to screen environmental agents that inhibit DNA topo 2 has been established and new inhibitors are being identified routinely.