Pod1um-201: A Phase Ii Study Of Retifanlimab (Incmga00012) In Advanced Or Metastatic Merkel Cell Carcinoma (Mcc)

Retifanlimab is a humanized IgG4 monoclonal antibody targeting human programmed cell death protein (PD)-1. Retifanlimab monotherapy as 500 mg intravenously (IV) every 4 weeks (Q4W) is under investigation in phase II studies in solid tumors. Here we report preliminary clinical activity and safety results from POD1UM-201, a phase II, open-label, single-arm, multicenter study assessing efficacy and safety of retifanlimab in advanced/metastatic MCC. Eligible patients (pts) have unresectable locally advanced/metastatic MCC, ECOG PS ≤1, measurable disease per RECIST v1.1, are either chemotherapy (chemo)-naïve or have received ≤3 prior chemo regimens, and have had no prior treatment with anti–PD-1/anti–PD-L1 therapy. The primary endpoint is overall response rate (ORR) per RECIST v1.1 in chemo-naïve pts. Secondary endpoints include safety in all pts, and duration of response (DOR), disease control rate, progression-free survival, and overall survival in chemo-naïve pts. As of January 8, 2020, 27 pts with MCC had received retifanlimab 500 mg IV Q4W (22 chemo-naïve, 5 refractory, all stage IV). Of the 22 chemo-naïve pts enrolled, 18 have had ≥1 on-study tumor assessment or discontinued. There are 10 (56%) responders (investigator assessed) with 2 (11%) complete responses and 8 (44%) partial responses. Of these, 6 are confirmed and 4 are unconfirmed ongoing responses. Three pts (17%) have stable disease. Among all treated pts (n=27), 16 (59%) had a treatment-emergent adverse event (TEAE); 6 (22%) were ≥Grade 3, 11 (41%) had a treatment-related TEAE (TRAE), 3 (11%) of which were ≥Grade 3. The most common TRAEs were asthenia and pruritus (n=3 each). Seven (26%) had a TEAE of special interest (the only immune-related AE occurring in >1 pt was hypothyroidism [n=2]). Two pts (7%) discontinued treatment due to TEAEs (radiculopathy and polyarthritis). No fatal TEAEs have been reported. Initial results demonstrate promising activity and safety of retifanlimab in pts with advanced or metastatic chemo-naïve MCC. Updated results from a preplanned analysis for futility will be presented at the meeting.