ABSTRACT: Merkel cell carcinoma (MCC) is a rare, aggressive, primary cutaneous neuroendocrine tumor that typically presents as an indurated nodule on sun-exposed areas of the head and neck in the white population. Major risk factors include immunosuppression, UV light exposure, and advanced age. Up to 80% of MCC are associated with Merkel cell polyomavirus. About 50% of patients present with localized disease, and surgical resection with or without adjuvant radiotherapy is generally indicated in this context. However, recurrence rates are high and overall prognosis rather poor, with mortality rates of 33%-46%. MCC is a chemosensitive disease, but responses in the advanced setting are seldom durable and not clearly associated with improved survival. Several recent trials with checkpoint inhibitors (pembrolizumab, avelumab, nivolumab) have shown very promising results with a favorable safety profile, in both chemonaïve and pretreated patients. In 2017, avelumab was approved by several regulatory agencies for the treatment of metastatic MCC, the first drug to be approved for this orphan disease. More recently, pembrolizumab has also been approved by the U.S. Food and Drug Administration in this setting. Immunotherapy has therefore become the new standard of care in advanced MCC. This article reviews current evidence and recommendations for the diagnosis and treatment of MCC and discusses recent therapeutic advances and their implications for care in patients with advanced disease. This consensus statement is the result of a collaboration between the Spanish Cooperative Group for Neuroendocrine Tumors, the Spanish Group of Treatment on Head and Neck Tumors, and the Spanish Melanoma Group. IMPLICATIONS FOR PRACTICE: Merkel cell carcinoma (MCC) is an uncommon aggressive skin cancer associated with advanced age, UV light exposure, and immunosuppression. Up to 80% are associated with Merkel cell polyomavirus. MCC is a chemosensitive disease, but tumor responses in the advanced setting are short-lived with no long-term survivors. Recent clinical trials with immune checkpoint inhibitors (i.e., pembrolizumab, avelumab, nivolumab) have shown promising results, with avelumab becoming the first drug to receive regulatory approval for this orphan indication. Further follow-up is needed, however, to define more adequately the long-term benefits of these drugs, and continued research is warranted to optimize immunotherapeutic strategies in this setting.
