3815

KIT

C-Kit|CD117|PBT|SCFR;v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog;KIT;v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog

mast/stem cell growth factor receptor Kit|p145 c-kit|piebald trait protein|proto-oncogene c-Kit|proto-oncogene tyrosine-protein kinase Kit|soluble KIT variant 1|tyrosine-protein kinase Kit|v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene-like protein

4q11-q12

protein-coding

Once a poorly defined pathologic oddity, in recent years, gastrointestinal stromal tumor (GIST) has emerged as a distinct oncogenetic entity that is now center stage in clinical trials of kinase-targeted therapies. This review chartsthe rapid progress that has established GIST as a model for understanding the role of oncogenic kinase mutations in human tumorigenesis. Approximately 80% to 85% of GISTs harbor activating mutations of the KIT tyrosine kinase. In a seriesof 322 GISTs (including 140 previously published cases) studied by the authors in detail, mutations in the KIT gene occurred with decreasing frequency in exons 11(66.1%), 9 (13%), 13 (1.2%), and 17 (0.6%). In the same series, a subset of tumors had mutations in the KIT-related kinase gene PDGF receptor alpha (PDGFRA), which occurred in either exon 18 (5.6%) or 12 (1.5%). The remainder of GISTs (12%) were wild type for both KIT and PDGFRA. Comparative studies of KIT-mutant,PDGFRA-mutant, and wild-type GISTs indicate that there are many similarities between these groups of tumors but also important differences. In particular, the responsiveness of GISTs to treatment with the kinase inhibitor imatinib varies substantially depending on the exonic location of the KIT or PDGFRA mutation. Given these differences, which have implications both for the diagnosis and treatment of GISTs, we propose a molecular-based classification of GIST. Recent studies of familial GIST, pediatric GIST, and variant forms of GIST related to Carney's triad and neurofibromatosis type 1 are discussed in relationship to this molecular classification. In addition, the role of mutation screening in KIT andPDGFRA as a diagnostic and prognostic aid is emphasized in this review.

The proto-oncogene c-kit is a receptor tyrosine kinase recognized to initiate essential signal transduction pathways that transmit biological signals for cellular proliferation, differentiation, and metastasis. Aberrant expression or mutation of c-kit has been shown to be involved in the pathogenesis of many cancers. Studies using imatinib mesylate (STI 571, Gleevec, Novartis, East Hannover, NJ, USA), an inhibitor of the tyrosine kinases brc-abl, c-kit, and PDGFR, have shown significant response in patients with chronic myelogenous leukemia and gastrointestinal stromal tumor. With the aim of identifying additional groups of tumors that may use the stem cell factor/c-kit pathway and,secondarily, may be responsive to imatinib mesylate treatment, we looked at the expression of c-kit in medulloblastoma. Medulloblastoma, a highly invasive primitive neuroectodermal tumor of the cerebellum, is the most common, malignantcentral nervous system tumor of childhood. Histologic features of medulloblastoma have failed to provide an accurate prediction of the clinical-biological behavior of these tumors. Characterizing the genetic events that play a role in the biology of these tumors may allow for molecular sub-typing and could lead to thedevelopment of novel therapeutic strategies. This study evaluated c-kit expression and mutational status in 10 medulloblastoma tumor samples. ALL 10 medulloblastoma tumors expressed c-kit by reverse transcriptase-polymerase chainreaction and 9 by immunohistochemical analysis. ALL tumor samples were screened for mutations in exons 9, 11, and 13 of the c-kit gene by direct sequencing. No sequence abnormalities were detected in these exons. These experiments lead us to the conclusion that c-kit activation in medulloblastoma is independent of mutation.

PURPOSE: Since the recent development of biologic agents targeting oncogenes, increasing attention has been focused on determining the role of tyrosine kinasereceptors in the pathogenesis of tumors. Our study was designed to investigate the status of region 4q12, which contains the candidate gene c-kit, and the expression of c-kit by immunohistochemistry (IHC). PATIENTS AND METHODS: Paired blood and biopsy specimens of 68 children treated for high-grade primary osteosarcomas were collected. Microsatellite analysis at two genomic sites containing c-kit gene was performed on paired DNA using a sensible fluorescent polymerase chain reaction technology. To confirm the DNA data, we studied c-kit protein expression by IHC in 56 available paraffin-embedded tumor tissues. RESULTS: The frequency of allelic imbalance (AI) at locus 4q12 was 39% in the overall population. In agreement with previous studies, we did not detect microsatellite instability, allowing us to hypothesize that this pathway is not implicated. Furthermore, the normal status at locus 4q12 was associated with a significantly better survival in the whole osteosarcoma population (P = .05). IHC overexpression of c-kit was concordant in ALL cases presenting an AI. However, normal status at locus 4q12 was correlated to an absence of c-kit protein expression in 19 (65.5%) of 29 informative cases. CONCLUSION: Allelotyping of locus 4q12, which contains the c-kit gene, could help pediatric osteosarcoma prognostic screening and showed a strong correlation with overexpression of c-kit protein. These results allowed us to hypothesize that, in some cases, a mutationof c-kit gene could lead to a protein overexpression.

Gastrointestinal stromal tumors (GISTs) are mesenchymal tumors of the intestinaltract that typically occur in adults over the age of 40 years. GISTs in younger patients are rare and not well characterized. The objective was to define the characteristics of GISTs in children and young adults (<30 years old). Clinicopathologic and molecular features, including KIT/PDGFRA genotype, in GISTs from 5 children and 10 young adults were analyzed. Gene expression analysis was performed on 5 gastric tumor samples from 2 children, 2 gastric tumors from young adults, and 10 gastric GISTs from older adults using an U133A Affymetrix platform (22,000 genes). ALL five pediatric GISTs occurred in girls, involved the stomachas multiple nodules, showed predominantly an epithelioid morphology, often involved lymph nodes, and lacked KIT or PDGFRA mutations. Although ALL five patients developed recurrence (four in the liver, three in the peritoneum, and two in both sites), four are still alive with disease. Of the 10 GISTs in young adults, half occurred in the small bowel and had spindle cell morphology, and one case had lymph node metastasis. KIT mutations were identified in seven cases, four in exon 11 and three in exon 9. Seven patients developed recurrence, and atlast follow-up two patients had died of disease. Gene expression analysis showedhigh expression of PHKA1, FZD2, NLGN4, IGF1R, and ANK3 in the pediatric and young adult versus older adult cases. GISTs that occur in children are a separate clinicopathologic and molecular subset with predilection for girls, multifocal gastric tumors, and wild-type KIT/PDGFRA genotype. In contrast, GISTs in young adults are a more heterogeneous group, including cases that resemble either the pediatric or the older adult-type tumors. The distinct gene expression profile suggests avenues for investigation of pathogenesis and potential therapeutic strategies.

The use of a relatively nontoxic tyrosine kinase receptor inhibitor, imatinib mesylate (IM) (STI-571), has increasingly become a valuable therapeutic alternative in some KIT (CD117)-overexpressing neoplasms potentially because of the presence of KIT-activating mutations. As the treatment eligibility for this drug hinges on CD117 expression, KIT immunostaining has recently been widely examined in various different tumors. We examined CD117 expression in pediatric embryonal rhabdomyosarcomas (RMSs) to identify its eventual prognostic impact and to evaluate its effect on tumorigenesis. This study included two spindle cell (leiomyomatous) variants, two botryoid variants, and 21 conventional embryonal RMSs. Sections from paraffin-embedded tumor samples were immunostained by a standard SABC technique using c-kit polyclonal antibody with antigen retrieval. In ALL the series, the percentage of CD117 positivity was 12%. Staining was strong in two of two spindle cell variants, in zero of two botryoid variants, and in one of 21 conventional embryonal RMSs. In Spearman's correlation analysis, there was statistical relationship between the presence of CD117 expression and the histological subtype of RMS. Kaplan-Meier analysis revealed no prognostic significance of CD117 expression for survival. The present study demonstrated a very limited expression of CD117 in pediatric embryonal RMS other than in the spindle cell variant. This finding suggested that the stem cell factor/c-kit pathway may be implicated in the tumorigenesis of spindle cell RMSs. Therefore, the mutation of c-kit gene must be prospectively examined in larger series of RMSs. If it can be verified that tissue expression of CD117 reflects the mutation of c-kit gene, IM can be considered a targeted therapy for CD117-expressing RMSs, particularly the spindle cell variant.

Neuroblastoma (NB) is the most common malignant solid tumor in childhood. There are well-recognized prognostic factors in NB such as age at diagnosis, organ of origin, stages, MYCN gene amplification, and expression of H-ras, trkA and survivin. Moreover, we investigated the expression of vascular endothelial growth factor (VEGF), tyrosine hydroxylase (TH), p53, stem cell factor (SCF) and c-kit of its receptor with quantitative real-time polymerase chain reaction (PCR) in 22 NBs and 4 other tumors (one malignant lymphoma, one malignant teratoma, and 2 rhabdomyosarcomas) samples. The correlation between patients' prognoses and the expression of TH or c-kit was newly recognized, particularly the good prognosis in patients in whom c-kit highly expressed and the poor prognosis contrarily associated with low or no expression, although the SCF of its ligand had no relationship with patient prognosis. It is possible that tumors without c-kit expression can not react with SCF (via the autocrine or paracrine system) and remain immature. It may be that this is a new critical clinical event in NB patients.

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors in the gastrointestinal tract. Approximately 85% of GISTs harbor activating mutations in the KIT or platelet-derived growth factor receptor alpha (PDGFRA) gene and approximately 95% of GISTs are positive for KIT (CD117) by immunohistochemistry. Nevertheless, approximately 5% of GISTs lack KIT expression. Inhibition of KIT and PDGFRA by tyrosine kinase inhibitors has revolutionized the treatment of GISTs and demands accurate tumor classification.DOG1.1 is a recently described mouse monoclonal antibody reported to have superior sensitivity and specificity compared with KIT (CD117) and CD34. We evaluated this new antibody on a group of 81 GISTs obtained from 74 patients with special regard to KIT-negative GISTs (n=28), pediatric GISTs (n=11), and GISTs associated with neurofibromatosis type I (NF1) (n=16). Conventional GISTs (n=26)were also included. ALL conventional KIT-positive GISTs, ALL NF1-associated GISTs, and 9/11 pediatric GISTs expressed DOG1.1. DOG1.1 was expressed in 10/28 (36%) of KIT-negative tumors. The staining pattern was cytoplasmic and/or membranous. This study demonstrates that DOG1.1 is a sensitive immunohistochemical marker for GIST, comparable with KIT, with the additional benefit of detecting 36% of KIT-negative GISTs. DOG1.1 is also a sensitive marker for unusual GIST subgroups lacking KIT or PDGFRA mutations. In tumors that are negative for both KIT and DOG1.1, mutational screening may be required to confirm the diagnosis of GIST.

An 18-year-old girl presented with abdominal pain and a tumor was subsequently detected in the jejunum. We therefore carried out a wedge resection of the jejunum. The diagnosis of GIST was confirmed histologically, and a mutation in exon 9 of the c-kit gene was observed. GISTs are rare in pediatric populations and pediatric GISTs occur predominantly in females and are characterized by a multifocal gastric location and a wild-type phenotype for the c-kit genes. The features of pediatric GISTs of the small intestine have not yet been categorized, and to date, only 11 cases in patients younger than 18 years have been reported.These cases did not occur primarily in females and tended to present as single tumors with mutations in the c-kit gene. This suggests that these cases do not have the same features as pediatric gastric GISTs, but instead are similar to adult GISTs. In pediatric populations, GISTs of the small intestine were expected to show a better response to imatinib treatment than gastric GISTs because of the alterations in the c-kit gene.

Familial gastrointestinal stromal tumor (GIST) syndrome is a rare autosomal dominant genetic disorder. We report on a kindred in which 3 family members carry a germline mutation (c.1727T>C, p.L576P) in exon 11 of the KIT gene. This mutation was not reported so far in familial GISTs. Apart from multiple GISTs in2 of the mutation carriers, ALL of them had multiple hyperpigmented skin maculesand a history of achalasia-like stenosis of the esophagus in early childhood. Inthe index patient >100 tumors and a diffuse Cajal cell hyperplasia of the small bowel occurred. Sequencing of DNA extracted from tumor tissue of one of his GISTs revealed the KIT mutation in exon 11 (c.1727T>C). By array comparative genomic hybridization whole chromosomal gains 3, 5, 7, 9, 12, 15, and 18 were detected. In addition, we could identify a gain on chromosome 4, spanning the KIT gene. Together with the family described here, 24 unrelated cases with proven germlinemutations in KIT have been reported. In these families the diagnosis was established from the age of 30 years onwards. Because in 1 patient reported herethe GIST was a coincidental finding at the age of 15 years, the tumors might occur at a very young age and remain unnoticed until they-either due to increasing size, ulceration, or malignant progression-become symptomatic. Therefore, we propose to start screening patients with known KIT mutations from a younger age.

Studies on gastrointestinal stromal tumors (GISTs) in young patients are limiteddue to their rarity, and none have been conducted in Asian populations. GISTs from patients under the age of 30 were retrospectively reviewed and were analyzed for clinicopathologic features, immunohistochemistry for SDHB (succinate dehydrogenase subunit B), and mutations for exon 9, 11, 13, and 17 of KIT gene and exon 12, 14, and 18 of PDGFRA gene. We found two pediatric (<18 years old) and 20 young adult (18-30 years old) GIST cases. pediatric GISTs occurred in twogirls, both as solitary masses with epithelioid histology in the stomach. Both GISTs were wild type for KIT and PDGFRA genes, were negative for SDHB, and therewas no recurrence during follow-up. Of the 20 GISTs in young adults, 12 (60%) were from extra-gastric locations (six duodenum, five jejunum, and one esophagus), and 16 (80%) showed a spindle cell morphology. mutations of KIT or PDGFRA genes were identified in 14 (78%) of the 18 cases. One patient with multiple gastric GISTs with perigastric lymph node metastases at presentation developed multiple distant metastases and died of the disease 7.3 years after diagnosis. Of the 19 R0-resected young adult patients, one patient with small intestinal GIST harboring KIT exon 11 deletion mutation developed recurrence andshowed partial responses for imatinib. In summary, compared with pediatric GIST cases, young adult GISTs are heterogeneous and share the characteristics of bothpediatric and adult GISTs. When a mesenchymal tumor is clinically suspected in the small intestine of young adults, a GIST should be included in the differential diagnoses. Further mutation studies and extensive treatments are recommended for these cases.#CI- (c) 2013 APMIS. Published by John Wiley & Sons Ltd.