Background: The anti–PD-1 antibody pembro showed efficacy and manageable safety in the global phase 2 KEYNOTE-224 and phase 3 KEYNOTE-240 studies of patients (pts) with previously treated advanced HCC, a population of high unmet need. KEYNOTE-394 is a randomized, double-blind, phase 3 study conducted in Asia to evaluate the efficacy and safety of pembro vs placebo, both given with BSC, as second-line therapy for previously treated advanced HCC (NCT03062358). Methods: Eligible pts in Asia with confirmed advanced HCC and progression on or intolerance to sorafenib or oxaliplatin-based chemotherapy were randomized 2:1 to pembro 200 mg or placebo Q3W for ≤35 cycles plus BSC per local guidelines. The primary endpoint was OS. Secondary endpoints were PFS, ORR, DOR, DCR, and TTP, all assessed per RECIST v1.1 by blinded independent central review, and safety. Treatment differences were assessed using the stratified log-rank test (OS and PFS) or the stratified Miettinen & Nurminen method (ORR). The P value boundary for OS superiority at final analysis (FA) was 0.019307. If OS was superior, PFS and ORR superiority at the second interim analysis (IA2; primary analysis timepoint for these endpoints) could be tested at boundaries of 0.013447 and 0.009139, respectively. Results: 453 pts were randomized to pembro (N = 300) or placebo (N = 153). Baseline characteristics were generally balanced between arms; 90.7% had received sorafenib as first-line therapy. As of the June 30, 2021 cutoff date for FA, median study follow-up was 33.8 mo (range 18.7-49.0). At FA, pembro significantly improved OS vs placebo (HR 0.79, 95% CI 0.63-0.99, P = 0.0180); median (95% CI) OS was 14.6 mo (12.6-18.0) for pembro vs 13.0 mo (10.5-15.1) for placebo and 24-mo OS rate was 34.3% vs 24.9%. At IA2, pembro significantly improved PFS (HR 0.74, 95% CI 0.60-0.92, P = 0.0032) and ORR (estimated difference 11.4%, 95% CI 6.7-16.0, P = 0.00004); median (95% CI) PFS was 2.6 mo (1.5-2.8) for pembro vs 2.3 mo (1.4-2.8) for placebo, 12-mo PFS rates were 15.9% vs 1.4%, and ORR was 12.7% vs 1.3%. At FA, ORR was 13.7% vs 1.3%, median DOR was 23.9 mo vs 5.6 mo, DCR was 52.7% vs 47.7%, and median TTP was 2.7 mo vs 1.7 mo (HR 0.72, 95% CI 0.58-0.90). At FA, treatment-related AEs occurred in 66.9% of pts in the pembro arm and 49.7% in the placebo arm, including 14.4% and 5.9% with grade 3-5 events. 3 pts (1.0%) in the pembro arm and 0 in the placebo arm died of treatment-related AEs. Conclusions: Pembro plus BSC significantly improved OS, PFS, and ORR compared with placebo plus BSC as second-line therapy for patients from Asia with advanced HCC. The pembro safety profile was as expected. Overall, results were consistent with those previously observed in KEYNOTE-224 and KEYNOTE-240 and thus add to the body of evidence supporting the use of pembro as second-line therapy for advanced HCC. Clinical trial information: NCT03062358.