c-Kit/PDGFRA Gene Status Alterations Possibly Related to Primary Imatinib Resistance in Gastrointestinal Stromal Tumors

Purpose Gastrointestinal stromal tumors (GISTs) commonly harbor oncogenic mutations of the KIT or platelet-derived growth factor alpha (PDGFRA) kinases, which are targets for imatinib. In clinical studies, 75% to 90% of patients with advanced GISTs experience clinical benefit from imatinib. However, imatinib resistance is an increasing clinical problem. Patients and Methods One hundred forty-seven patients with advanced, unresectable GISTs were enrolled onto a randomized, phase II clinical study of imatinib. Specimens from pretreatment and/or imatinib-resistant tumors were analyzed to identify molecular correlates of imatinib resistance. Secondary kinase mutations of KIT or PDGFRA that were identified in imatinib-resistant GISTs were biochemically profiled for imatinib sensitivity. Results Molecular studies were performed using specimens from 10 patients with primary and 33 patients with secondary resistance. Imatinib-resistant tumors had levels of activated KIT that were similar to or greater than those typically found in untreated GISTs. Secondary kinase mutations were rare in GISTs with primary resistance but frequently found in GISTs with secondary resistance (10% v 67%; P = .002). Evidence for clonal evolution and/or polyclonal secondary kinase mutations was seen in three (18.8%) of 16 patients. Secondary kinase mutations were nonrandomly distributed and were associated with decreased imatinib sensitivity compared with typical KIT exon 11 mutations. Using RNAi technology, we demonstrated that imatinib-resistant GIST cells remain dependent on KIT kinase activity for activation of critical downstream signaling pathways. Conclusion Different molecular mechanisms are responsible for primary and secondary imatinib resistance in GISTs. These findings have implications for future approaches to the growing problem of imatinib resistance in patients with advanced GISTs.

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Imatinib in the Management of Multiple Gastrointestinal Stromal Tumors Associated With a Germline KIT K642E Mutation

Archives of Pathology & Laboratory Medicine ◽

10.5858/2007-131-1393-iitmom ◽

2007 ◽

Vol 131 (9) ◽

pp. 1393-1396

Author(s):

Janet Graham ◽

Maria Debiec-Rychter ◽

Christopher L. Corless ◽

Robin Reid ◽

Rosemarie Davidson ◽

...

Keyword(s):

Gastrointestinal Stromal Tumors ◽

Interstitial Cells Of Cajal ◽

Germline Mutations ◽

Mesenchymal Tumors ◽

Stromal Tumors ◽

Pdgfra Gene ◽

Oncogenic Mutations ◽

Esophageal Tumors ◽

Exon 11 ◽

Cells Of Cajal

Abstract Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gut and are distinguished by expression of CD117 (c-Kit). Oncogenic mutations in the KIT or PDGFRA gene are detected in approximately 85% of sporadic GISTs. In recent years, examples of familial GIST have been reported in which germline mutations of KIT or PDGFRA result in multiple GISTs, skin disorders, and other abnormalities. The most common germline mutations are in KIT exon 11, mutations in exons 8 and 17 have also been described, and there are 2 families with germline PDGFRA mutations. We present a case in which a germline KIT exon 13 mutation (K642E) was discovered in a patient with multiple GISTs of rectum, small intestine, and esophagus, as well as diffuse hyperplasia of the interstitial cells of Cajal. To our knowledge, this is only the second germline example of this particular mutation. The patient's esophageal tumors were stabilized with imatinib.

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