Merkel cell carcinoma (MCC) is a rare, aggressive neuroendocrine cancer of the skin with a mortality of approximately 33%. Approximately one-third of patients present with metastatic disease, for which there is no effective treatment. Merkel cell polyomavirus (MCV), a DNA virus that expresses T antigen oncoproteins, was found to be clonally integrated into the genome of the majority of MCC tumors. MCC tumor progression is believed to be associated with the development of immune evasion, and multiple lines of evidence (higher incidence in immunocompromised populations, reports of spontaneous regression, responses to immune modulators, and improved prognosis associated with CD8+ intratumoral lymphocytes) suggest that immunotherapy may improve outcomes in patients with advanced MCC. Ipilimumab is a recombinant, human monoclonal antibody that binds to cytotoxic Tlymphocyte- associated antigen 4 and has shown efficacy in metastatic melanoma.