A phase II trial of imatinib mesylate in Merkel cell carcinoma (neuroendocrine carcinoma of the skin): A Southwest Oncology Group Study (S0331)

9056 Background: Merkel cell carcinoma (MCC, neuroendocrine carcinoma of the skin) frequently stains strongly for c-KIT (CD-117) expression. We therefore evaluated imatinib mesylate as a treatment for MCC. Methods: Eligibility included patients with measurable metastatic or unresectable MCC with CD117 expression by immunostaining. A Zubrod performance status of 0–2, adequate hematologic, renal, and hepatic function was also required. Imatinib 400 mg daily was administered orally in 28-day cycles. Results: A total of 25 patients were accrued to this trial from 13 institutions, with 6 accrued through Intergroup participation by the Eastern Cooperative Oncology Group. Two patients were ineligible (one was found not to express CD117 on central pathology review, and one lacked measurable disease). These 23 patients were included in the analysis. Imatinib was well tolerated with Grade 1 or 2 nausea, diarrhea, and hematologic toxicity as the most frequent side effects. There were no complete responses (0%) and 1...