Background: Immunotherapy approaches, including immune checkpoint blockade, have shown initial promising results in HCC. Anti PD-1 therapy with pembrolizumab has demonstrated antitumor activity and manageable safety in multiple cancers. KEYNOTE-224 (NCT02702414), an open label, phase 2 trial assessed the efficacy and safety of pembrolizumab in pts with advanced HCC previously treated with sorafenib. Methods: Eligible pts were age ≥18 y with confirmed HCC, radiographic progression after sorafenib and disease not amenable to curative treatment, Child Pugh A, ECOG PS 0-1 and predicted life expectancy > 3 mo. Pts received pembrolizumab 200 mg Q3W for 2 y or until disease progression, unacceptable toxicity, withdrawal of consent or investigator decision. Response was assessed every 9 wk (RECIST v1.1, central review). Primary endpoint was ORR (RECIST v1.1, central review). Secondary endpoints included DOR, DCR, PFS, OS, and safety and tolerability. Data cutoff date was Aug 24, 2017. Results: Of 104 treated pts, 23 continued therapy (median follow up 8.4 mo, range 0.4-13.6). Median age of pts was 68y (range 43-87), 21.2% were HBV⁺, 26% were HCV⁺, 94.2% were Child Pugh A, 79.8% had PD on sorafenib and 63.5% had extrahepatic disease. ORR was 16.3% (95% CI, 9.8 to 24.9) and similar across subgroups with different etiology. Median time to response was 2.1 mo (range 1.8-4.8) and 94% of responders were estimated to have a response duration ≥6 mo. Best responses were CR in 1 patient (1.0%), PR in 16 (15.4%), SD in 47 (45.2%) and PD in 34 (32.7%); DCR was 61.5%. Median PFS was 4.8 mo (95% CI, 3.4 to 6.6) and median OS (9.4 to NA) was not reached. The 6 mo PFS and OS rates were 43.1% and 77.9%, respectively. Treatment related (TR) AE occurred in 73.1% of pts; fatigue (21.2%) and increased aspartate aminotransferase (12.5%) were seen in ≥10% of pts and grades 3-5 TRAE in 25% including 1 death (ulcerative esophagitis). No cases of HBV/HCV flare occurred; immune mediated hepatitis occurred in 3 (2.9%) pts. Conclusion: Pembrolizumab treatment resulted in durable responses and favorable PFS and OS in pts with advanced HCC previously treated with sorafenib. Safety was generally comparable to that established for pembrolizumab monotherapy. Clinical trial information: NCT02702414