Avelumab in chemotherapy-refractory metastatic Merkel cell carcinoma: Subgroup analysis of efficacy.

80Background: Merkel cell carcinoma (MCC) is a rare, aggressive skin cancer. In a phase 2 trial in previously treated metastatic MCC (mMCC; JAVELIN Merkel 200, NCT02155647), avelumab, a fully human IgG1 anti–PD-L1 antibody, showed durable responses and a manageable safety profile, including confirmed objective response rate (ORR) of 31.8% (95.9% CI 21.9-43.1), 6-mo duration of response (DOR) rate estimate of 92%, and 6-mo progression-free survival (PFS) rate of 40% (95% CI 29-50). We report post-hoc subgroup analyses from this trial. Methods: Pts with mMCC and prior disease progression on chemotherapy received avelumab 10 mg/kg (1h IV) Q2W. Tumors were assessed every 6 wks (RECIST v1.1) by independent review. Kaplan-Meier method was used to estimate 6-mo DOR and PFS rate. Results: 88 pts were treated with avelumab and followed for ≥ 6 mos (data cutoff Mar 3, 2016). Responses occurred in all subgroups analyzed (Table). Trends of higher ORR and 6-mo PFS rates were seen in pts with fewer prior lines, lower d...