Complete responses (CR) in patients receiving atezolizumab (atezo) + bevacizumab (bev) versus sorafenib (sor) in IMbrave150: A phase III clinical trial for unresectable hepatocellular carcinoma (HCC).

4596 Background: In the Phase III IMbrave150 trial, statistically significant and clinically meaningful improvements in OS and PFS were seen with atezo + bev vs sor in pts with unresectable HCC who had not received prior systemic therapy (Cheng, ESMO Asia, 2019). Historically, CR rates have been low in HCC clinical trials. Here we report the baseline characteristics for IMbrave150 pts with a CR. Methods: IMbrave150 enrolled systemic treatment-naive pts with unresectable HCC. Pts were randomized 2:1 to receive either atezo 1200 mg IV q3w + bev 15 mg/kg IV q3w or sor 400 mg BID until unacceptable toxicity or loss of clinical benefit per investigator. Co-primary endpoints were OS and PFS by independent review facility (IRF)–assessed RECIST 1.1. The key secondary endpoints IRF ORR per RECIST 1.1 and IRF ORR per HCC mRECIST were also part of the study statistical testing hierarchy. Results: The ITT population included 336 pts randomized to atezo + bev and 165 pts randomized to sor. With a median follow-up of 8.6 mo (data cutoff, Aug 29, 2019), OS HR was 0.58 (95% CI: 0.42, 0.79; P = 0.0006) and PFS HR was 0.59 (95% CI: 0.47, 0.76; P < 0.0001) with atezo + bev vs sor. ORR was 27% vs 12% ( P < 0.0001) per IRF RECIST 1.1 and 33% vs 13% ( P < 0.0001) per IRF HCC mRECIST with atezo + bev vs sor, respectively. For responders (per IRF RECIST 1.1), median time to response was 2.8 mo (range, 1.2-11.3) with atezo + bev and 3.3 mo (range, 1.2-7.2) with sor. CR per IRF-assessed RECIST 1.1 was achieved by 18 pts in the atezo + bev arm and 0 pts in the sor arm. The baseline characteristics for atezo + bev CR pts are shown in the table. Additional characteristics will be shown. Conclusions: IMbrave150 demonstrated statistically significant and clinically meaningful improvement in both OS and PFS with atezo + bev vs sor in pts with unresectable HCC who have not received prior systemic therapy. Pts achieved CRs regardless of poor prognostic factors or etiology. Atezo + bev may be a practice-changing treatment for pts with unresectable HCC. Clinical trial information: NCT03434379 . [Table: see text]