Background: HCC is one of the most commonly diagnosed cancers globally. Most cases occur in Asia, although a number of patients (pts) are affected in Europe and North America. In the phase 3, open-label RATIONALE-301 trial (NCT03412773), TIS, a PD-1 inhibitor, showed non-inferior overall survival (OS) versus SOR (hazard ratio 0.85, 95% CI: 0.71, 1.02), and a favorable safety profile, in 1L treatment of pts with unresectable HCC. Here, efficacy and safety of TIS versus SOR in the RATIONALE-301 EU/NA subgroup were compared with the overall population (OP). Methods: Systemic therapy-naïve adults with histologically confirmed HCC were randomized (1:1) to receive TIS (200 mg IV Q3W) or SOR (400 mg orally BID) until disease progression, intolerable toxicity, or withdrawal. The primary endpoint was OS; secondary endpoints included objective response rate (ORR), progression-free survival (PFS), and duration of response (DoR) by blinded independent review committee per RECIST v1.1, and safety. Results: In the EU/NA subgroup (172/674 pts randomized), at data cutoff (July 11, 2022), median (m) OS follow-up was 37.9 months (mo) (TIS) vs 38.5 mo (SOR). At baseline, fewer pts in the EU/NA subgroup had Barcelona Clinic Liver Cancer (BCLC) Stage C disease (70% vs 78%) and extrahepatic spread (51% vs 62%), and more had a non-viral etiology (60% vs 24%) or underlying HCV infection (28% vs 13%) than in the OP, respectively. Distribution of other baseline characteristics was generally similar between the EU/NA subgroup and the OP. Efficacy data in the EU/NA subgroup were consistent with the OP. Numerically longer mOS and mDoR, higher ORR, and similar mPFS were observed with TIS versus SOR in the EU/NA subgroup. In the EU/NA safety population, incidence of ≥grade 3 treatment-emergent adverse events (TEAEs; 46% vs 66%), ≥grade 3 treatment-related TEAEs (TRAEs; 17% vs 50%), and TRAEs leading to discontinuation (9% vs 15%) was lower with TIS versus SOR, respectively, similar to the OP. Conclusions: In the RATIONALE-301 EU/NA subgroup, mOS of TIS was non-inferior versus SOR, consistent with the findings from the OP. Numerically longer mOS and mDoR, and a higher ORR was seen with TIS versus SOR in the EU/NA subgroup, which had a higher rate of pts with non-viral etiology and a slightly lower number of pts with advanced-stage disease (BCLC Stage C) compared with the OP. Clinical trial information: NCT03412773.

Intent-to-treat analysis set; data cutoff: July 11, 2022. CI, confidence interval; NE, not evaluable.