A knock-in mouse model of gastrointestinal stromal tumor harboring kit K641E

A mouse model of gastrointestinal stromal tumor (GIST) has been developed by a knock-in gene targeting strategy, which introduced a Kit gene K641E mutation, originally identified in sporadic human GISTs and in the germ line of familial GIST syndrome patients. Homozygous and heterozygous Kit K641E mice develop gastrointestinal pathology with complete penetrance and all Kit K641E homozygotes die by age 30 weeks due to gastrointestinal obstruction by hyperplastic interstitial cells of Cajal (ICC) or GISTs. Heterozygous mice have less extensive ICC hyperplasia and smaller GISTs, suggesting a dose-response relationship between oncogenically activated Kit and ICC proliferation. Immunoprecipitation and Western blotting reveal GISTs to contain abundant phosphorylated/activated Kit. In addition to ICC hyperplasia and GISTs, homozygous Kit K641E mice exhibit loss-of-function Kit phenotypes, including white coat color, decreased numbers of dermal mast cells, and sterility, indicating that despite its oncogenic activity the mutant form cannot accomplish many activities of the wild-type gene. Kit K641E reproduces the pathology associated with the familial GIST syndrome and thus is an excellent model to study Kit pathway activation, ICC biology, GIST pathogenesis, and preclinical validations of GIST therapies and mechanisms of drug resistance.

Multiple gastrointestinal stromal tumors with a germline c-kit mutation

Familial gastrointestinal stromal tumor (GIST) is a rare autosomal dominant genetic disorder; thus far, only seven families have been reported with c-kit germline mutations. Presented herein is a case of multiple intestinal GIST in a 38-year-old man with a germline mutation of the c-kit gene. Operative specimens of the jejunal segment and multiple wedge resection specimens included approximately 30 masses, ranging in size from 1.0 to 6.0 cm. Microscopically, the tumors were composed of CD117-positive spindle/epitheloid cells with variable numbers of mitotic counts, a characteristic of GIST. The mitotic rate increased to more than 5/50 high-power fields. Interestingly, marked hypertrophy of the myenteric plexus with CD117-positive cells was identified in the intestinal segment. By polymerase chain reaction-single-strand conformation polymorphism analysis and direct DNA sequencing, a heterozygous c-kit missense mutation at nucleotide 1676 of codon 559 (T --> C, Val --> Ala), part of the juxtamembrane domain, was detected in the normal tissue. The same mutation was homozygous in the tumor samples. The present case is the first proven case of multiple GIST with a c-kit germline mutation in Korea and is distinguishable from other reported germ-line c-kit mutations because the same 1676 T --> C missense mutation occurs in the normal allele as well as the affected allele, although the significance of the identical mutations remains to be investigated.

[Recommendations for the management of GIST patients]

BACKGROUND

The management of gastrointestinal stromal tumors (GIST) has evolved very rapidly in the last years. A national consensus meeting was therefore organized in order to identify the optimal management procedures for patients with GIST in localized and advanced stages.

METHODS

A panel of different specialties, including pathology, molecular biology, imaging, surgery, gastroenterology, medical oncology reviewed the current literature, in particular the recent Lugano conference, to identify consensus points and topics for future research in four different working groups: pathology and molecular biology, early management of small tumors and imaging, surgery, and medical treatment. Consensus points were categorized according to the Standard Options Recommendations (SOR) of the French Federation of Cancer Centers.

RESULTS

The standard histological examination with immunohistochemical analysis using CD117, CD34, PS100, desmin and smooth muscle actin is considered standard. Molecular biology for the identification of KIT and PDGFRA mutation is advisable for GIST with negative CD117 staining, and otherwise is considered a research procedure. Complete tumor resection with negative tumor margins is the standard surgical treatment. Adjuvant imatinib after optimal tumor resection as well as neo-adjuvant imatinib remain experimental approaches to be performed within prospective clinical studies. Imatinib should be started at the date of diagnosis of metastatic relapse and given until development of intolerance or progressive disease. Resection of metastases is also considered as an experimental procedure which can not be recommended routinely. The criteria for tumor response to imatinib should include not only tumor size reduction or disease stabilization, but also reduction of tumor density (Hounsfield units) on computed tomography, metabolic activity (i.e. reduction of FDG uptake on positron emission tomography), and reduction of vascularisation of the tumors using contrast enhanced ultrasound evaluation. An increase in tumor size may be associated with pathologic response to imatinib therapy, and available survival data indicate that the survival of these patients is similar to that of patients with conventional tumor response.

CONCLUSIONS

Consensus points in clinical management of GIST in this national conference adopted the majority of consensus points published in the Lugano conference. This multidisciplinary work will be published in the reference oncology, gastroenterology, and pathology journals in French languages.

Differential expression of connexin 43 in gastrointestinal stromal tumours of gastric and small intestinal origin

Gastrointestinal stromal tumours (GISTs) are considered to originate from interstitial cells of Cajal (ICCs). ICCs are classified into several subtypes according to their location or roles. Several reports indicate that GISTs of the small intestine appear to have different clinical and pathological characteristics from gastric GISTs. We previously found using a cDNA expression chip that connexin 43, a component of gap junctions, is expressed specifically in small intestinal GISTs but not in gastric GISTs. To confirm the specificity of connexin 43 expression, we analysed 10 small intestinal GISTs and 15 gastric GISTs by northern blotting, western blotting and immunohistochemistry in this study. Northern blotting was performed in five small intestinal GISTs and five gastric GISTs, and revealed connexin 43 mRNA expression in all of the five small intestinal GISTs, but in none of the gastric GISTs. By western blotting, bands corresponding to connexin 43 were easily detected in all of the five small intestinal GISTs studied but were absent in all five gastric GISTs analysed. Immunohistochemistry showed that all of the 10 small intestinal GISTs were positive for connexin 43 but only one of 15 gastric GISTs, which exhibited a mutation in exon 9 of the KIT gene, was connexin 43-positive. We also examined the localization of connexin 43 in the normal stomach and small intestine. Immunoreactivity for connexin 43 was present in both normal gastric and small intestinal circular muscle layers, but it was unclear which cell type was positive. These results suggest that GISTs are divided into at least two groups, namely the gastric subtype and the small intestinal subtype, through phenotype but not location. Furthermore, these data indicate that the gastric and the small intestinal subtypes of GIST may originate from different subtypes of ICC.

Deletions affecting codons 557-558 of the c-KIT gene indicate a poor prognosis in patients with completely resected gastrointestinal stromal tumors: a study by the Spanish Group for Sarcoma Research (GEIS)

PURPOSE

To explore the prognostic value of mutations in c-KIT and PDGFR-alpha genes with respect to relapse-free survival (RFS) in patients with gastrointestinal stromal tumors (GIST). We have investigated the prognostic relevance of the type and position of the mutations, in addition to other clinicopathologic factors, in a large series of patients with GIST.

METHODS

For this study, 162 patients were selected according to the following criteria: completely resected tumors with negative margins attended between 1994 and 2001; no metastasis at diagnosis; tumor larger than 2 cm, c-KIT-positive immunostaining; and no other primary tumors.

RESULTS

The median follow-up was 42 months for patients free of recurrence. Mutations were detected in 96 tumors (60%): 82 cases involving c-KIT and 14 cases involving PDFGR-alpha. Univariate analysis demonstrated the following as poor prognostic factors for RFS: tumors larger than 10 cm (P < .0001); mitotic count higher than 10 mitoses per 50 high-power fields (P < .0001); high risk index (P < .0001); intestinal GIST location (P = .0041); high cellularity (P < .0001); tumor necrosis (P < .0001); deletions affecting exon 11 (P = .0007); and deletions affecting codons 557 to 558 (P < .0001). After the multivariate analysis, only the high risk index (relative risk [RR], 12.36), high cellularity (RR, 3.97), and deletions affecting codons 557 to 558 of c-KIT (RR, 2.57) corresponded to independent prognostic factors for RFS in GIST patients.

CONCLUSION

Deletions affecting codons 557 to 558 are relevant for the prognosis of RFS in GIST patients. This critical genetic alteration should be considered to be a new prognostic stratification variable for randomized trials exploring imatinib mesylate in the adjuvant setting in GIST patients.

No GIST-type c-kit gain of function mutations in neuroblastic tumours

AIMS

Neuroblastic tumours (NTs) have been shown to respond to imatinib treatment in vivo and in vitro, possibly via inactivating the c-kit receptor. The purpose of this study was to identify gastrointestinal stromal tumour (GIST)-type c-kit gene associated mutations in exons 9, 11, 13, and 17 in NTs to recognise a subset of tumours that would probably respond to imatinib treatment.

METHODS

Expression of the c-kit protein was detected immunohistochemically in a total of 37 archival paraffin wax embedded NTs using polyclonal rabbit antihuman c-kit antibody. After immunohistochemistry, c-kit gene associated chromosomal mutations in all cases of NT were detected with denaturing high performance liquid chromatography (HPLC).

RESULTS

Denaturing HLPC analysis did not reveal GIST-type mutations in four immunohistochemically detected c-kit positive or in 33 c-kit negative NTs.

CONCLUSIONS

c-kit receptor expression and GIST-type c-kit gene mutations are rare events in NTs. Oncogenic activation of c-kit in NTs presumably differs from that of GISTs, which may influence their responsiveness to imatinib treatment. Whether c-kit has an essential role in the pathogenesis of NTs remains to be investigated.

Novel germline mutation of KIT associated with familial gastrointestinal stromal tumors and mastocytosis

Gastrointestinal stromal tumors (GISTs) are often associated with activating KIT mutations, affecting regulatory domains of the KIT tyrosine kinase. Sporadic mastocytosis in adults is usually also caused by KIT mutations that, however, activate KIT by affecting the intracellular enzymatic site of the molecule. Most GISTs respond to KIT inhibitors that bind to the enzymatic site; in most cases of mastocytosis, however, the modified enzymatic site is not affected by these drugs. We present a kindred with both familial GISTs and mastocytosis that express a novel germline KIT mutation in exon 8, resulting in deletion of codon 419 and affecting the extracellular domain of KIT. This mutation activates KIT, and the mutant KIT is inhibited by the tyrosine kinase inhibitor imatinib mesylate. Our studies identify a new regulatory region in the KIT molecule and strongly suggest that patients with extracellular KIT mutations respond to tyrosine kinase inhibitors.

Effects of imatinib vary with the types of KIT-mutation in gastrointestinal stromal tumor cell lines

Mutations of proto-oncogene c-kit in gastrointestinal stromal tumors (GISTs) are considered to cause a constitutive activation of KIT responsible for their oncogenesis. Imatinib has therapeutic potential for GISTs because of its inhibitory effect on KIT kinase activity. However, no study has been published concerning the effects of imatinib on GIST cells with various types of KIT mutation. To investigate the effects of imatinib on various c-kit mutations found in GISTs, cell proliferation and apoptosis assays were performed in two GIST cell lines with different KIT mutations. One of the cell lines, GIST-T1, revealed a heterozygous deletion of exon 11 in the c-kit, while the other cell line, GIST882, possessed a homozygous missense mutation of exon 13 in the c-kit gene. Imatinib inhibited proliferation and induced apoptosis in both cell lines. Imatinib potently suppressed proliferation of the GIST882 cell line at the concentration of 1.0 microM, whereas it inhibited the GIST-T1 at 0.1 microM. In two types of activating mutant KIT, imatinib could inhibit the constitutive activation of both types of KIT mutant, although the antiproliferative effect on GIST882 was weaker than on GIST-T1. Western blot analysis revealed that apoptosis related proteins were activated or suppressed by imatinib in both cell lines in the respective manner. Our results suggest that the apoptotic signal trans-duction caused by imatinib in GISTs is susceptible to various types of KIT mutation.

Acquired resistance to imatinib in gastrointestinal stromal tumor occurs through secondary gene mutation

Most gastrointestinal stromal tumors (GIST) have an activating mutation in either KIT or PDGFRA. Imatinib is a selective tyrosine kinase inhibitor and achieves a partial response or stable disease in about 80% of patients with metastatic GIST. It is now clear that some patients with GIST develop resistance to imatinib during chronic therapy. To identify the mechanism of resistance, we studied 31 patients with GIST who were treated with imatinib and then underwent surgical resection. There were 13 patients who were nonresistant to imatinib, 3 with primary resistance, and 15 with acquired resistance after initial benefit from the drug. There were no secondary mutations in KIT or PDGFRA in the nonresistant or primary resistance groups. In contrast, secondary mutations were found in 7 of 15 (46%) patients with acquired resistance, each of whom had a primary mutation in KIT exon 11. Most secondary mutations were located in KIT exon 17. KIT phosphorylation was heterogeneous and did not correlate with clinical response to imatinib or mutation status. That acquired resistance to imatinib in GIST commonly occurs via secondary gene mutation in the KIT kinase domain has implications for strategies to delay or prevent imatinib resistance and to employ newer targeted therapies.

9p21 locus analysis in high-risk gastrointestinal stromal tumors characterized for c-kit and platelet-derived growth factor receptor alpha gene alterations

BACKGROUND

Gastrointestinal stromal tumors (GISTs) are noncomplex sarcomas that often are due to c-kit-activating and platelet-derived growth factor receptor alpha gene (PDGFRalpha)-activating mutations and perturbations of their related signaling pathways. Molecular and cytogenetic findings have indicated correlations between tumor progression and high-risk GISTs with c-kit mutations, the overexpression of genes such as ezrin, and losses at 9p. In particular, it was reported recently that malignant GISTs showed alterations in the p16INK4a gene located at the 9p21 locus.

METHODS

To assess the involvement of p14ARF and p15INK4b in addition to p16INK4a in GISTs, the authors undertook a molecular and cytogenetic study of the 9p21 locus. A series of 22 pre-Gleevec era, cryopreserved, high-risk GISTs that were characterized well in terms of KIT and PDGFRalpha receptors were investigated for mRNA expression, homozygous deletions, mutations, and promoter methylation of locus 9p21, in some instances complemented by fluorescent in situ hybridization studies.

RESULTS

The results indicated the loss of p16INK4a mRNA expression in 41% of the GISTs, mainly due to the homozygous deletion of both the p16INK4a gene and the p14ARF gene (24%). No mutations were found, and promoter methylation (detected by means of methylation-specific polymerase chain reaction analysis in 27% of tumors) was restricted mainly to the p15INK4b gene (20%). It is noteworthy that, in all of the methylated GISTs, the epigenetic promoter alteration was coupled with mRNA expression.

CONCLUSIONS

Alterations in the 9p21 locus were found cumulatively in 54% of the tumors in the current series and were represented mainly by the loss of tumor suppressor gene expression. The p16INK4a deletion, which always was coupled with p14ARF gene loss, seemed to be the most common 9p21 inactivation mechanism.

The location of KIT and PDGFRA gene mutations in gastrointestinal stromal tumours is site and phenotype associated

AIMS

To assess the relation between KIT and PDGFRA mutations and the site of origin, histological phenotype, and pathomorphologically determined risk assessment in gastrointestinal stromal tumours (GISTs).

METHODS

A series of 83 clinicopathologically characterised GISTs from 79 patients was analysed for KIT and PDGFRA mutations by polymerase chain reaction amplification, single strand conformation polymorphism analysis, and direct DNA sequencing.

RESULTS

KIT or PDGFRA mutations were found in 57 and 11 GISTs, respectively. Most KIT mutations involved exon 11 (46 cases), followed by exon 9 (10 cases). The PDGFRA mutations mostly affected exon 18 (eight cases), followed by exon 12 (three cases). There was a significant association between KIT exon 9 mutations and an intestinal origin of GISTs, and between PDGFRA mutations and gastric origin of the tumours. In addition, the presence of PDGFRA mutations was significantly associated with epithelioid/mixed histology, as was the absence of identified receptor tyrosine kinase mutations. Vice versa, KIT exon 11 mutations were almost exclusively found in spindle cell GISTs. Furthermore, the presence of any KIT and PDGFRA mutations and the presence of KIT mutations alone were significantly associated with high risk/malignant GISTs.

CONCLUSIONS

The location of KIT and PDGFRA mutations in GISTs is associated with the site of origin and histological phenotype. Genotyping of GISTs may be a helpful additional parameter in determining the biological profile of these tumours.

Gastrointestinal stromal tumors of neurofibromatosis type I (von Recklinghausen's disease)

Gastrointestinal stromal tumor (GIST), as well as the hyperplastic lesions of intestinal neural tissue and its supporting structures, is a gastrointestinal complication of type 1 neurofibromatosis (NF1) (von Recklinghausen's disease). In the present study, we analyzed the histologic and immunohistochemical features, and the c-kit and PDGFRA gene mutations of 36 GISTs derived from 9 NF1 patients. Distinctively, multiple GISTs arose preferentially in the small intestine. The histologic features of NF1-associated GISTs are almost similar to those of non-NF1 GISTs, but characteristically most of the NF1-associated GISTs contained skeinoid fibers. Thirty-three GISTs (92%) showed immunoreactivity for KIT, and 23 tumors (64%) showed diffuse or mosaic-like immunoreactivity for S-100 protein. Hyperplasic lesions, which may be the hyperplasia of interstitial cells of Cajal, were observed around some GISTs. Exons 9, 11, 13, and 17 of the c-kit gene and exons 12 and 18 of the PDGFRA gene were amplified and directly sequenced. Point mutations of c-kit gene or PDGFRA gene were identified only in three (8%) and two (6%) tumors, respectively. NF1-associated GISTs, showing the dual differentiation of interstitial cells of Cajal and Schwann cells, develop in close association with the myenteric nerve structure of gastrointestinal tract of NF1 patients. The point mutations of c-kit and PDGFRA gene may play a limited role in the tumorigenesis of NF1-associated GISTs.

A recurrent duodenal gastrointestinal stromal tumor with a frameshift mutation resulting in a stop codon in KIT exon 13

Gastrointestinal stromal tumors (GISTs) are a specific and rare subset of human gastrointestinal tract tumors. Most GISTs show gain-of-function mutations of KIT, mainly in exon 11, that always maintain the reading frame. We report on data from a 43-year-old Japanese man with recurrent duodenal GIST and a frameshift mutation in KIT exon 13 together with an in-frame deletion in KIT exon 11 detected by genomic DNA sequencing. Deletion of 48 base pairs of KIT exon 11, which preserved the reading frame, was identified in both primary and recurrent tumors, whereas deletion of one nucleotide of codon 642 of KIT exon 13, which changed the reading frame and induced a novel stop codon at amino acid 644, was found only in the recurrent tumor. The predicted protein resulting from the latter would lack part of the kinase domain. To the best of our knowledge, this is the first documentation of a GIST with a frameshift mutation of KIT.

Prognostic value of KIT mutation in gastrointestinal stromal tumors

AIM: To examine the prevalence and prognostic significance of C-kit gene mutation and analysis the correlation of C-kit gene mutation and the clinicalpathologic parameters of GISTs.

METHODS: Eighty-two GISTs were studied for the mutation of C-kit gene by PCR-SSCP, DNA sequence. Statistical comparison were used to analysis the correlation of C-kit gene mutation and clinicalpathology, clinical behavior, recurrence.

RESULTS: (1) Mutation-positive and mutation-negative GISTs were 34 and 48,respectively; (2) Among these patients with C-kit mutation remained a significantly poor prognosis associated with 59% 3-year survival compared to those whose tumors did not; (3) Tumor size, PCNA index, mitotic cell number, presence of necrosis, microscopic invasion to adjacent tissues, recurrence and distant metastasis among mutation-positive and mutation-negative GISTs were significantly different.

CONCLUSION: C-kit mutation is a undoubtedly pivotal event in GIST and may be associated with poor prognosis. Evaluation of C-kit gene mutation may have both prognosis and therapeutic significances.

Patterns of gene amplification in gastrointestinal stromal tumors (GIST)

Gastrointestinal stromal tumors (GIST) are the most common primary mesenchymal tumors of the gastrointestinal tract (GIT). They represent a wide clinico-pathological spectrum of tumors. No single histological or clinical parameter can predict the prognosis while the response to therapy is related to the type of KIT or PDGFRA mutation. Cytogenetic and CGH studies have identified frequent gross chromosomal aberrations but the target genes of these changes are unknown. To determine whether known oncogenes take part in genomic rearrangements and to investigate the potential clinical significance of their amplifications, nine known oncogenes (CMYC, MDM2, GLI1, CDK4, HER2, EGFR1, CCND1, FGF3, EMS) were analyzed by fluorescent in situ hybridization (FISH) on a tissue microarray (TMA) containing 94 primary GIST. Clinical follow-up information was available for 57 of these patients. Amplification was found for CMYC in three of 90 (3.3%), for MDM2 in five of 94 (5.3%), for EGFR1 in five of 94 (5.3%), and for CCND1 in seven of 79 (8.9%) evaluable cases. No amplifications were seen for HER2, GLI1, CDK4, FGF3, and EMS. Amplifications of MDM2 and CCND1 were associated with clinical and histological malignancy. In conclusion, our data show that gene amplification does occur in a subset of GIST. Identification of MDM2/CCND1 amplification may represent another molecular feature that could help in the evaluation of the behavior of GISTs.

Clinical and molecular characteristics of pediatric gastrointestinal stromal tumors (GISTs)

BACKGROUND

To describe the clinical characteristics, molecular features, treatment, and outcome of six pediatric patients with gastrointestinal stromal tumors (GISTs).

PATIENTS AND METHODS

Retrospective clinical review of GISTs, seen at The Hospital for Sick Children (HSC) Toronto, over an 11-year period. All specimens were stained for the CD 117 and CD 34 antigens. Three specimens were sequenced for mutations in exons 9, 11, and 13 of the c-kit gene.

RESULTS

Five patients were evaluated and treated at HSC and one was referred for histopathological consultation only. The median patient age at diagnosis was 13.6 years, (6.9-14.8 years); four were female. All patients presented with anemia secondary to gastrointestinal (GI) bleeding. The disease was localized in five patients and two had other malignancies consistent with the diagnoses of Carney's triad. Immunohistochemical staining for CD 117 and CD 34 showed heavy cytoplasmic localization in all of the tumor cells. A novel point mutation of KIT in codon 456 of exon 9 was found in one case. Complete surgical resection was achieved in the five patients managed at our center and none received adjuvant therapies. Disease recurred locally in one patient. Four patients are alive and one is lost to follow-up.

CONCLUSIONS

In children and adolescents, GISTs should be considered in the differential diagnosis of anemia secondary to GI hemorrhage. The absence of an exon 11 mutation and the identification of a novel mutation in exon 9 suggest that pediatric GISTs may respond differently to currently available targeted therapies and therefore should be studied within the context of collaborative group trials.

Gastric cancer: new genetic developments

Gastric cancer's (GC) incidence shows large geographic differences worldwide with the lowest rates occurring in most Western industrialized countries including the United States and the United Kingdom; in contrast, relatively high rates of GC occur in Japan, Korea, China, and South America, particularly Chile. The Laurén classification system classifies GC under two major histopathological variants: 1) an intestinal type and 2) a diffuse type. The intestinal type is more common in the general population, more likely to be sporadic and related to environmental factors such as diet, particularly salted fish and meat as well as smoked foods, cigarette smoking, and alcohol use. It exhibits components of glandular, solid, or intestinal architecture, as well as tubular structures. On the other hand, the diffuse type is more likely to have a primary genetic etiology, a subset of which, known as hereditary diffuse gastric cancer (HDGC), is due to the E-cadherin (CDH1) germline mutation. The diffuse type pathology is characterized by poorly cohesive clusters of cells which infiltrate the gastric wall, leading to its widespread thickening and rigidity of the gastric wall, known as linitis plastica. Helicobacter pylori infection is associated with risk for both the intestinal and diffuse varieties of gastric cancer. Germline truncating mutations of the CDH1 gene, which codes for the E-cadherin protein, were initially identified in three Maori families from New Zealand that were predisposed to diffuse GC. Since then, similar mutations have been described in more than 40 additional HDGC families of diverse ethnic backgrounds. It is noteworthy that two-thirds of HDGC families reported to date have proved negative for the CDH1 germline mutation. A number of candidate genes have been identified through analysis of the molecular biology of E-cadherin. Patients with evidence of the CDH1 germline mutation in the context of a family history of HDGC must be considered as candidates for prophylactic gastrectomy, given the extreme difficulty in its early diagnosis and its exceedingly poor prognosis when there is regional or distant spread. Specifically, the E-cadherin cytoplasmic tail interacts with catenins, assembling the cell-adhesion complex involved with E-cadherin mediated cell:cell adhesion. Beta-catenin and gamma-catenin compete for the same binding site on the E-cadherin cytoplasmic tail, directly linking the adhesion complex to the cytoskeleton through alpha-catenin. Beta-catenin gene (CTNNB1) mutations have been described predominantly in intestinal-type gastric cancers and CTNNB1 gene amplification and overexpression have recently been described in a mixed-type gastric cancer. This paper reviews the genetics of both intestinal and diffuse types of gastric carcinoma, their differential diagnosis, molecular genetics, pathology, and, when known, their mode of genetic transmission within families.

[c-kit and PDGFRA mutations in 60 cases of gastrointestinal stromal tumors (GISTs)]

OBJECTIVE

To explore the status of activating mutations of c-kit and PDGFRA in GIST of Chinese patients.

METHODS

Sixty GISTs, confirmed by immunoreactivity of CD117, CD34, SMA, S-100 and Desmin, were evaluated for the presence of c-kit exons 9, 11, 13 and 17 mutations, and PDGFRA exons 12 and 18 mutations. The PCR products were sequenced directly for mutations, using DNA extracted from paraffin-embedded tissue.

RESULTS

53% of the tumors were located in the stomach, 22% in the small bowel, 8% in the colo rectum, 2% in the esophagus and 15% in the extragastrointestinal tract. Immunohistochemical demonstrations of c-kit (CD117) were seen in 90% cases. Overall, c-kit mutations were detected in 63.3% of patients as follows: 58.3% in exon 11, 3.3% in exon 9, 1.7% in exon 13 and none in exon 17. The types of c-kit exon 11 mutations were mostly heterogeneous and clustered in the classic "hot spot" at the 5' end of exon 11, 42.9% being point mutation and in-frame deletion at Codon 557-560. 14.3% of cases showed internal tandem duplications (ITD) at the 3' end of exon 11 in a region of a second hot spot for c-kit mutations. Interestingly, these cases were associated with female predominance, stomach location and occurrence in older patients. The present study failed to identify a significant association between c-kit mutation status and risk of aggressive behavior in GISTs. Exon 9 mutations consisted of ITP of six nucleotides encoding Ala-Tyr. A new point mutation of L641P was revealed in exon 13. PDGFRA mutations were found in 5% of all the 60 cases with none of the positive cases expressed detectable KIT protein. The type of mutation was the commonest point mutation of D842V of exon 18.

CONCLUSION

Most KIT expressing GIST show c-kit mutations that are preferentially located within the classic hot spot of exon 11. A second hot spot -ITD at the 3' end of exon 11 seems to associate with a subgroup of gastric GISTs in older females. c-kit exons 9, 13 and 17 mutations are rare events in GIST of China. PDGFRA oncogenic mutations are more likely seen in KIT-negative GISTs arising in the peritoneal surface and have an unfavorable clinical course.

Gastrointestinal Stromal Tumors Express ras Oncogene

BACKGROUND

Gastrointestinal stromal tumors (GISTs) constitute the largest category of nonepithelial neoplasms of the gastrointestinal tract. Histologically, they have a spindle cell appearance but stain by immunohistochemistry for the proto-oncogene, c-kit (CD117). There is some evidence that phosphorylation of these receptors leads to a cascade that may activate the ras/mitogen-activated protein kinase pathway, which may, in turn, allow other oncogenes to become active.

HYPOTHESIS

Immunohistochemical staining pattern of GISTs will aid in their differentiation from other spindle cell tumors and predict clinical outcome in patients.

DESIGN AND SETTING

Retrospective review of patient records and paraffin block specimens of spindle cell tumors.

PATIENTS

We have identified 65 patients with spindle cell tumors of the gastrointestinal tract at our institution in the past 10 years. Tumors were diagnosed by their morphology as leiomyomas, leiomyoblastomas, or leiomyosarcomas.

MAIN OUTCOME MEASURES

CD117 and ras p21 were stained by immunohistochemistry on formalin-fixed, paraffin-embedded sections of normal and tumor tissues.

RESULTS

Of the 65 patients, there were 23 patients diagnosed as having GIST confirmed by CD117 expression and 42 patients without GIST. Gastrointestinal stromal tumor samples of 17 (77%) of 22 patients stained positive for ras protein compared with 0 of 27 patients with leiomyomas (P<.001).

CONCLUSIONS

To our knowledge, this study is the first to demonstrate that GISTs stain positive for ras p21. This molecular trait may be a useful diagnostic tool in addition to the c-kit (CD117) to separate GISTs from leiomyomas and leiomyosarcomas. In the future, ras inhibitors may potentially be a therapeutic to treat GISTs.

Epithelioid Gastrointestinal Stromal Tumor With PDGFRA Activating Mutation and Immunoreactivity

The authors report a unique case of an intra-abdominal, epithelioid mesenchymal tumor that had an activating mutation of PDGFRA and a strong PDGFRA immunoreactivity but lacked both c-kit mutation and c-kit protein (CD117) expression. IHC study showed that the tumor cells were diffusely and strongly positive for PDGFRA, vimentin, CD34, and Bcl-2 but completely negative for CD117 as well as for muscle, epithelial, endothelial, endocrine, mesothelial, neural, and melanocytic cell markers. Molecular study revealed a mutation at the juxtamembrane domain of exon 12 in PDGFRA gene with GTC to GAC transition at codon 561 (V561D), as shown in the previous mutational studies on gastrointestinal stromal tumor (GIST). This case likely represents an example of GIST with PDGFRA activating mutation and PDGFRA immunoreactivity without CD117 positivity, which has not been documented in the literature. STI 571 (imatinib mesylate [Gleevec]) might be an effective therapy in this case, since Gleevec targets both PDGFRA and c-kit oncoproteins.

KIT overexpression and amplification in gastrointestinal stromal tumors (GISTs)

The tyrosine kinase receptor KIT plays a major role in gastrointestinal stromal tumors (GISTs) oncogenesis. Indeed, 95% of GISTs express KIT protein, and about 70% exhibit activating mutations of the KIT gene. However, little is known about KIT overexpression mechanisms in these tumors, and the correlation with KIT mutations. GISTs with mutations within exon 11 (n=12) or 9 (n=1) of KIT were compared with GISTs without KIT mutations in exons 9, 11, 13, and 17 (n=10), two of them had PDGFRA mutations. KIT amplification was studied by real-time PCR of KIT and beta-ACTIN genes, and by fluorescence in situ hybridization (FISH) using KIT and chromosome 4 centromere specific probes. KIT transcripts and protein expression were quantified by reverse transcription real-time PCR and Western blot respectively. Genomic analysis revealed a single mutated GIST with KIT amplification. KIT protein and RNA levels were highly variable in GISTs but closely correlated (r=0.82, P<1.10(-5)), and were higher in GISTs with KIT mutations (P=0.07 and P=0.03 respectively). In conclusion, contrasting with the regulation of other tyrosine kinase receptors, KIT overexpression in GISTs is rarely related to a gene amplification, which suggests a deregulation of KIT gene transcription.

PDGFRA mutations in gastrointestinal stromal tumors: frequency, spectrum and in vitro sensitivity to imatinib

PURPOSE

Gastrointestinal stromal tumors (GISTs) commonly harbor oncogenic mutations of the KIT tyrosine kinase, which is a target for the kinase inhibitor imatinib. A subset of GISTs, however, contains mutations in the homologous kinase platelet derived growth factor receptor alpha (PDGFRA), and the most common of these mutations is resistant to imatinib in vitro. Little is known of the other types of PDGFRA mutations that occur in GISTs.

MATERIALS AND METHODS

We determined the KIT and PDGFRA mutation status of 1,105 unique GISTs using a combination of denaturing high-performance liquid chromatography and direct sequencing.

RESULTS

66 in exon 18, 11 in exon 12, and three in exon 14. Transient expression of representative PDGFRA isoforms in CHO cells revealed imatinib sensitivity of exon 12 mutations (SPDHE566-571R and insertion ER561-562) and an exon 14 substitution (N659K). However, most isoforms with a substitution involving codon D842 in exon 18 (D842V, RD841-842KI, DI842-843IM) were resistant to the drug, with the exception of D842Y. Interestingly, other mutations in exon 18 (D846Y, N848K, Y849K and HDSN845-848P) were all imatinib sensitive. Proliferation studies with BA/F3 cell lines stably expressing selected PDGFRA mutant isoforms supported these findings.

CONCLUSION

Including our cases, there are 289 reported PDGFRA-mutant GISTs, of which 181 (62.6%) had the imatinib-resistant substitution D842V. However, our findings suggest that more than one third of GISTs with PDGFRA mutations may respond to imatinib and that mutation screening may be helpful in the management of these tumors.