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 to 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 to 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.