LAUSR

e21006 Background: MCC is an aggressive neuroendocrine carcinoma of the skin. Avelumab (anti-PD-L1) was FDA approved for the treatment of metastatic MCC based on an overall response rate (ORR) of 32% in chemotherapy-refractory pts. In first line, responses to PD1/PD-L1 have been reported in 56-62% of pts. Atezolizumab (Atezo) targets PD-L1 and bevacizumab (bev) inhibits VEGF. Pre-clinical data suggests atezo + bev improves antigen-specific T-cell migration, and encouraging clinical activity of this regimen has been reported in renal cell and hepatocellular carcinoma. Here we report safety and interim results of atezo + bev in MCC. Methods: In this phase II single-arm study the efficacy and safety of atezo + bev was evaluated in pts with recurrent/metastatic PD-1/PD-L1-inhibitor naive MCC. Patients were treated with atezo 1200 mg + bev 15 mg/kg IV Q3W. Primary endpoint was ORR (RECIST 1.1) by blinded independent radiologist. Secondary endpoints included ORR by iRECIST, PFS, DOR, DCR, OS, and safety. Results: 11 pts enrolled. Median age was 70 (range:57-84), (7) 63% were male, and 7 (63%) had been treated with curative intent. Five (45%) pts had received platinum/etoposide (2 in the neo-adjuvant setting and 3 in first-line). Median follow-up is 9.7 months (range:2.8-15.9). Adverse events (AEs) that occurred in > 1 pt: hypertension (7), proteinuria (3), fatigue (2), peripheral edema (2), epistaxis (2), and transaminitis (2). Grade 3 AEs: hypertension (2), proteinuria (1), and auto-immune hepatitis (1); all manageable. Only 1 subject discontinued treatment due to toxicity (auto-immune hepatitis). There were no grade > 3 AEs. Objective response occurred in 7 (64%) pts, including 3 (27%) complete responses (CR). One partial response was unconfirmed (patient discontinued treatment after 1 dose of atezo/bev due to grade 3 hepatitis). 4 pts remain on treatment (1 pt with CR withdrew consent for further therapy and has not recurred). Median PFS is 6.3 months (95% CI:4.5-NA). Conclusions: Atezo + bev was well tolerated in MCC pts. Safety was consistent with that of the individual agents. Activity is encouraging with 64% ORR (27% CR rate) and mPFS of 6.3 months. Clinical trial information: NCT03074513.