Adjuvant Therapy of Completely Resected Merkel Cell Carcinoma With Immune Checkpoint Blocking Antibodies vs Observation

Primary objective: To estimate the efficacy of adjuvant nivolumab monotherapy in completely resected MCC patients Primary endpoint: Disease-free survival (DFS) rate evaluated at 12, 24 and 48 months after date of randomization Secondary Objectives: To describe the safety profile and additional efficacy parameters of the nivolumab treatment in MCC Secondary endpoints: * Adverse events according to CTCAE, Version 4.0 criteria, that are related to the administration of nivolumab * Disease-free survival (DFS) * Overall survival (OS) and OS rates at 12, 24 and 48 months after randomization Explorative Endpoints: * Distant-metastases-free survival (DMFS) and DMFS rate at 12, 24 and 48 months after randomization * Identification and validation of prognostic/predictive biomarkers * Quality of life (EORTC QLQ-C30) until 24 months after randomization