First-line Serplulimab in Metastatic Colorectal Cancer: Phase 2 Results of a Randomized, Double-Blind, Phase 2/3 Trial

BackgroundWhether or not the addition of immunotherapy to current standard-of-care treatments can improve efficacy in proficient mismatch repair (pMMR)/microsatellite-stable (MSS) metastatic colorectal cancer (mCRC), the predominant type of mCRC, is unclear.MethodsThis randomized, double-blind, phase 2 part of a phase 2/3 trial was conducted at 23 hospitals across China (ClinicalTrials.gov: NCT04547166). Patients with unresectable metastatic/recurrent colorectal adenocarcinoma and no prior systemic therapy were randomly assigned 1:1 to receive every-3-weeks intravenous serplulimab (300 mg) plus HLX04 (7.5 mg/kg) and XELOX (serplulimab group) or placebo (300 mg) plus bevacizumab (7.5 mg/kg) and XELOX (placebo group). The primary endpoint was independent radiology review committee (IRRC)-assessed progression-free survival (PFS). Secondary endpoints included other efficacy endpoints and safety.FindingsBetween July 16, 2021, and January 20, 2022, 114 patients were enrolled and randomly assigned to the serplulimab (n = 57) or placebo (n = 57) group. All patients had stage IV CRC, and 95.7% of the patients with available microsatellite instability (MSI) status were MSS. With a median follow-up duration of 17.7 months, median PFS was prolonged in the serplulimab group (17.2 vs. 10.7 months; hazard ratio [HR], 0.60; 95% confidence interval [CI], 0.31–1.14). Although the median overall survival (OS) was not reached for either group, a trend of an OS benefit was observed for the serplulimab group (HR, 0.77; 95% CI, 0.41–1.45). 36 (65.5%) and 32 (56.1%) patients in the serplulimab and placebo groups had grade ≥3 treatment-related adverse events, respectively.ConclusionsSerplulimab plus HLX04 and XELOX exhibits promising efficacy and is safe and tolerable in patients with treatment-naive mCRC.FundingThis work was funded by Shanghai Henlius Biotech, Inc.