Background: In the phase III Orient-32 trial (NCT03794440), sintilimab plus IBI305 demonstrated a meaningful improvement in overall survival (OS) and progression-free survival (PFS) vs. sorafenib (Sor) in patients (pts) with unresectable HCC. Here we report the AESIs for sintilimab and IBI305 in Orient-32. Methods: 571 eligible pts with unresectable HCC were randomly assigned (2:1) to receive either sintilimab plus IBI305 or Sor (400 mg orally twice daily), until disease progression or unacceptable toxicity. The co-primary endpoints were OS and independent radiological review committee (IRRC)-assessed PFS according to RECIST 1.1. AESIs were defined by the sponsor and reported without judgement of causality. Analyses explored the incidence and severity of AESIs as well as correlation between AESIs and efficacy. Results: The safety set included 402 pts in the sintilimab plus IBI305 group and 184 pts in the Sor group. At the data cutoff on Dec 30th, 2021, the median follow-up time was 26.7 months. Any AESIs (≥1%) for sintilimab plus IBI305 group and Sor group occurred in 77.9% pts and 53.3% pts, respectively. The incidence of treatment-related grade 3-4 AESI for sintilimab+IBI305 was 31.3% and treatment-related serious AESI was 13.9%. The most common any AESIs were proteinuria (61.7% ), hypertension (41.8%), hemorrhage (15.4%) and hyperthyroidism (14.2%) (Table). In the characteristics of baseline, ages can be a predictor of the onset of proteinuria, hypertension and hyperthyroidism. In addition, the occurrence of of proteinuria and hypertension can be a predictor for a better survival. Conclusions: AESIs for sintilimab and IBI305 were tolerable and manageable in Orient-32 trial. Further, the incidence and severity of AESIs were consistent with the known safety profiles of the individual agents. Clinical trial information: NCT03794440.

^a In≥2% of pts.