We report the safety and efficacy of M7824 in Asian patients (pts) with pretreated BTC. Methods: Pts who progressed after 1 line of chemotherapy receive M7824 1200 mg q2w until disease progression, unacceptable toxicity, or trial withdrawal in this expansion cohort of the ongoing phase 1, open-label trial NCT02699515. The primary objective is safety/tolerability; secondary objectives include best overall response per RECIST v1.1. Results: At 39 wk median follow-up, 30 pts received M7824 for a median of 8.9 (range, 2.0-57.6) wk; 5 pts were on active treatment. Treatment-related adverse events (TRAEs) occurred in 60% of pts; most common were maculopapular rash and pyrexia (13.3% each), as well as lipase increase and rash (10.0% each). 10 pts (33.3%) experienced grade 3 TRAEs, including 3 grade 5 (1 septic shock [bacteremia, unknown etiology; 249 and 14 days after first and last dose, resp.], 2 due to interstitial lung disease [ILD; 1 on treatment post 3 doses, 1 after 6 mo of initial ILD diagnosis and last dose). Objective responses were observed in 7 pts (ORR, 23.3%; IHCC, 4/10 pts; EHCC, 1/7 pts; GC, 2/12 pts; AC, 0/1 pts), with 1 durable complete response (5.6þ mo) and 4/6 partial responses (PRs) ongoing at data cutoff (0.7þ, 2.8, 3.9þ, 5.5þ, 5.6, and 6.9þ mo). 1 additional pt with GC had an ongoing PR for 7.6þ mo after initial pseudoprogression. Conclusions: M7824 monotherapy has an acceptable safety profile and promising efficacy in Asian pts with pretreated BTC, with durable responses in 8/30 pts (27%; includes 1 pt with pseudoprogression) across BTC subtypes, including responses in pts with IHCC, EHCC, and GC (ORRs, 40%, 14%, and 17%, resp.). Editorial acknowledgement: Medical writing support was provided by ClinicalThinking and was funded by Merck KGaA,