First-line therapy with pembrolizumab yielded frequent and durable response in patients with advanced Merkel cell carcinoma, an aggressive type of skin cancer associated with ultraviolet light exposure and the Merkel cell polyomavirus (MCPyV), a study presented at the American Academy for Cancer Research (AACR) Annual Meeting 2016 has shown.1

Although cytotoxic chemotherapy is associated with high response rates in patients with metastatic Merkel cell carcinoma, responses are not typically durable and median progression-free survival is only 13 weeks. Because Merkel cell carcinoma may be responsive to programmed death-1 (PD-1) pathway inhibition, researchers sought to evaluate the efficacy and safety of the humanized IgG4 PD-1-blocking antibody pembrolizumab in patients with advanced/metastatic disease.

For the open-label, phase 2 trial, researchers enrolled 26 patients with advanced/metastatic Merkel cell carcinoma who had not received prior systemic therapy. Of those, 17 had MCPyV-positive disease. All participants received pembrolizumab 2 mg/kg intravenously every 3 weeks.

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“In this clinical trial, patients with metastatic Merkel cell carcinoma who received pembrolizumab had an objective response rate of 56%, which is similar to chemotherapy outcomes, but the duration of response to pembrolizumab appears to be significantly longer than that for chemotherapy,” said Paul Nghiem, MD, PhD, professor of medicine, Division of Dermatology at the University of Washington School of Medicine and an affiliate investigator of the Clinical Research Division at Fred Hutchinson Cancer Research Center in Seattle.

Results also showed that the overall response rate among patients with MCPyV-positive disease was 63% and 44% for those with virus-negative Merkel cell carcinoma. Three patients with virus-positive disease and 1 patient with virus-negative disease achieved a complete response. Seven and 3 patients, respectively, had partial responses.

“While the study is still ongoing, the vast majority of patients (86%) who responded to pembrolizumab are still experiencing excellent disease control more than 6 months after starting therapy,” he said.

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In terms of safety, treatment was generally well tolerated with most adverse events being grade 1 or 2. Two patients developed severe drug-related toxicities, both of which lessened with corticosteroid therapy and both patients continue to have ongoing tumor responses despite pembrolizumab discontinuation.

“Currently there are no FDA-approved drugs for the treatment of MCC. We are expanding this trial to recruit additional patients and we hope that these data will contribute to meaningful new therapeutic options becoming available for these patients,” Nghiem said.


  1. Nghiem P, Bhatia S, Lipson, et al. Durable, long-term survival in previously treated patients with advanced melanoma (MEL) who received nivolumab (NIVO) monotherapy in a phase I trial. Oral presentation at: AACR Annual Meeting 2016; April 16-20, 2016; New Orleans, LA.