Nivolumab (Nivo) as neoadjuvant therapy in patients with resectable Merkel cell carcinoma (MCC) in CheckMate 358.

9505Background: MCC is a rare, aggressive skin cancer commonly associated with the oncogenic Merkel cell polyomavirus (MCPyV). The PD-1/PD-L1 immunosuppressive pathway is often upregulated in MCC, and advanced metastatic MCC is responsive to PD-1 blockade. Here we report the first trial of anti–PD-1 in the neoadjuvant setting for resectable MCC. Methods: In the phase 1/2 CheckMate 358 trial of nivo anti–PD-1 in virus-associated cancers (NCT02488759), patients (pts) with resectable MCC received nivo 240 mg IV on D1 and D15. Surgery was planned on D29. Tumor regression was assessed radiologically before surgery, and microscopically in the surgical specimen. Immunohistochemistry (IHC) was used to assess tumor MCPyV status and tumor PD-L1 expression. Data were analyzed as of August 7, 2017 with a median follow-up of 54.1 wks. Results: 25 pts with resectable MCC, AJCC stage IIA–IV, received ≥1 dose of nivo. Median age was 70 yrs (range 22–88). Among 18 patients’ tumors evaluated by IHC, 8 (44%) were MCPyV+, an...