Efficacy and Safety of First-line Avelumab Treatment in Patients With Stage IV Metastatic Merkel Cell Carcinoma: A Preplanned Interim Analysis of a Clinical Trial.

Importance: Merkel cell carcinoma (MCC) is an aggressive skin cancer that is associated with poor survival outcomes in patients with distant metastatic disease. Results of part A of the JAVELIN Merkel 200 trial (avelumab in patients with Merkel cell carcinoma) showed that avelumab, an anti-programmed cell death ligand 1 (PD-L1) antibody, demonstrated efficacy in second-line or later treatment of patients with metastatic MCC (mMCC).

Objective: To evaluate the efficacy and safety of avelumab as first-line treatment for patients with distant mMCC.

Design, Setting, and Participants: JAVELIN Merkel 200 part B is an international, multicenter, single-arm, open-label clinical trial of first-line avelumab monotherapy. Eligible patients were adults with mMCC who had not received prior systemic treatment for metastatic disease. Patients were not selected for PD-L1 expression or Merkel cell polyomavirus status. Data were collected from April 15, 2016, to March 24, 2017, and enrollment is ongoing.

Interventions: Patients received avelumab, 10 mg/kg, by 1-hour intravenous infusion every 2 weeks until confirmed disease progression, unacceptable toxic effects, or withdrawal occurred.

Main Outcomes and Measures: Tumor status was assessed every 6 weeks and evaluated by independent review committee per Response Evaluation Criteria in Solid Tumors version 1.1. The primary end point was durable response, defined as an objective response with a duration of at least 6 months. Secondary end points include best overall response, duration of response, progression-free survival, safety, and tolerability.

Results: As of March 24, 2017, 39 patients were enrolled (30 men and 9 women; median age, 75 years [range, 47-88 years]), with a median follow-up of 5.1 months (range, 0.3-11.3 months). In a preplanned analysis, efficacy was assessed in 29 patients with at least 3 months of follow-up; the confirmed objective response rate was 62.1% (95% CI, 42.3%-79.3%), with 14 of 18 responses (77.8%) ongoing at the time of analysis. In responding patients, the estimated proportion with duration of response of at least 3 months was 93% (95% CI, 61%-99%); duration of response of at least 6 months, 83% (95% CI, 46%-96%). First-line avelumab treatment was generally well tolerated, and no treatment-related deaths or grade 4 adverse events occurred.

Conclusions and Relevance: High rates of response to first-line avelumab therapy in patients with distant mMCC build on previously reported antitumor activity after second-line or later treatment, and maturing progression-free survival data suggest that responses are durable. These data further support avelumab's approval in the United States and European Union and use as a standard-of-care treatment for mMCC.

Trial Registration: clinicaltrials.gov Identifier: NCT02155647.