Half of 25 patients with Merkel cell carcinoma treated with pembrolizumab experienced significant tumor shrinkage that lasted almost 3 times longer than conventional chemotherapy. Some of whom had no remaining disease after treatment, study results presented at the American Association for Cancer Research (AACR) 2016 Annual Meeting 2016 have shown.

Pembrolizumab is an immune checkpoint inhibitor. Merkel cell carcinoma is a rare, virus-linked skin cancer. Merkel cell carcinoma is diagnosed in less than 2000 people each year in the United States. It usually affects people with suppressed immune systems and the elderly. Approximately 80% of cases of Merkel cell carcinoma are caused by the Merkel cell polyomavirus, with the remainder caused by unknown factors and exposure to ultraviolet light.

More than 20% of all cancers worldwide are virus-linked; therefore, researchers hope that these results indicate a treatment benefit from an entire class of drugs.

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In this multicenter, phase II, non-controlled clinical trial, researchers enrolled 26 patients with metastatic or recurrent Merkel cell carcinoma who had not received any systemic therapies for advanced disease. In total, 17 of 26 patients had virus-positive tumors.

All patients had received standard therapy with surgery and/or radiation therapy. One patient received chemotherapy 6 months before the study began prior to the development of advanced disease, and 1 patient did not receive imaging scans in time for inclusion in the outcomes. Patients received 2 mg/kg of pembrolizumab every 3 weeks.

The objective response rate for the 25 patients with at least 1 evaluation during treatment was 56% (95% CI, 35-76%). Four patients experienced a complete response, and 10 patients experienced a partial response.

Median follow-up was 33 weeks (range, 7-53 weeks), and relapses occurred in 2 of 14 patients who had a response (14%). Duration of the response ranged from at least 2.2 months to at least 9.7 months. At 6 months, the rate of progression-free survival was 67% (95% CI, 49-86%).

Among patients with virus-positive disease, the response rate was 62% (10 of 16 patients). Among patients with virus-negative disease, the response rate was 44% (4 of 9 patients).

Objective response rate was 56%. Drug-related grade 3 or 4 adverse events occurred in 15% of all patients. Efficacy correlated with tumor viral status.

“What we found in this preliminary study of patients with Merkel cell cancer may not be true for every virus-induced cancer, but if additional studies with more patients confirm our findings, we will have strong reason to believe that many cancers with virus-linked proteins could be valid targets for immune checkpoint blockade.” said Suzanne Topalian, MD, professor of surgery and oncology and associate director of the Bloomberg-Kimmel Institute for Cancer Immunotherapy and Johns Hopkins School of Medicine, Baltimore, Maryland.


1. Nghiem PT, Bhatia S, Lipson EJ, et al. Clinical activity, immune and viral correlates of PD-1 blockade with pembrolizumab as first systemic therapy in patients with advanced Merkel cell carcinoma [published online ahead of print April 19, 2016]. N Engl J Med. doi:10.1056/NEJMoa1603702.