A Phase II Trial of Imatinib Mesylate in Merkel Cell Carcinoma (Neuroendocrine Carcinoma of the Skin): A Southwest Oncology Group Study (S0331)

BACKGROUND—Imatinib mesylate (Gleevec ® ) was evaluated as a treatment for Merkel cell carcinoma (MCC, neuroendocrine carcinoma of the skin) based on the identification of strong c-KIT staining of these neoplasms. METHODS—Eligibility included patients with measurable metastatic or unresectable MCC, c-KIT (CD117) expression and a Zubrod performance status of 0–2. Imatinib 400 mg daily was administered orally in 28-day cycles to 23 patients. RESULTS—Overall, imatinib was well tolerated with Grade 1 or 2 nausea, diarrhea, and hematologic toxicity as the most frequent side effects. A partial response was seen in 1 patient (4%; 95% CI: 0% – 22%). Median progression-free survival was 1 month (95% CI: 1–2 months). Median overall survival was 5 months (95% CI 2–8 months). One patient achieved a partial response and another had prolonged disease stabilization while receiving treatment. CONCLUSIONS—The majority of patients progressed rapidly within 1–2 cycles of treatment. The observed progression-free survival and overall survival were not adequate to conclude that this agent was active in advanced MCC, and thus the planned second stage of patient accrual was not opened.