ORIGINAL ARTICLE 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 unre-sectable 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 overal