First-line serplulimab plus HLX04 and XELOX versus placebo plus bevacizumab and XELOX in metastatic colorectal cancer: A phase 2/3 study.

Abstract

3569 Background: This is a randomized, double-blind, multicenter phase 2/3 study comparing the efficacy and safety of serplulimab (a novel anti-PD-1 antibody) plus HLX04 (an approved bevacizumab biosimilar) and XELOX chemotherapy vs. placebo plus bevacizumab and XELOX as first-line treatment for metastatic colorectal cancer (mCRC). Interim analysis presented at the 2024 ASCO Gastrointestinal Cancers Symposium showed improvement in progression-free survival (PFS), and duration of response (DOR) for the serplulimab arm. Here we present the updated results with an extended follow-up duration of 24.2 months and the subgroup analysis results. Methods: In the phase 2 part, 114 patients with mCRC and no prior systemic therapy were randomized 1:1 (serplulimab arm, n = 57; placebo arm, n = 57) to receive intravenous (IV) serplulimab (300 mg) plus HLX04 (7.5 mg/kg) and XELOX (IV oxaliplatin [130 mg/m2] and oral capecitabine [1000 mg/m2]) (group A) or placebo plus bevacizumab and XELOX (group B) once every 3 weeks. Stratification factors were PD-L1 expression level, ECOG PS score, and primary tumor site. The primary endpoint was independent radiological review committee (IRRC)-assessed PFS per RECIST 1.1. Secondary endpoints included other efficacy endpoints, safety, pharmacokinetics, biomarker explorations, and quality-of-life assessments. Results: By the data cutoff of December 15, 2023, continuing improvements in PFS (16.8 vs. 10.7 months; stratified HR 0.62, 95% CI 0.33–1.12) and DOR (19.4 vs. 12.6 months; stratified HR 0.33, 95% CI 0.13–0.85) were observed for group A compared to group B. 55/112 (49.1%) patients in the efficacy evaluable set has died; 24/55 (43.6%) patients in group A and 31/57 (54.4%) in group B. Median overall survival (OS) was not reached (NR) in group A, and 21.2 months in group B (stratified HR 0.75, 95% CI 0.43–1.30). Subgroup analysis showed similar trends towards an improved median OS for key subgroups including microsatellite stable (MSS) (NR vs. 21.2 months; stratified HR 0.73, 95% CI 0.39–1.37), KRAS-mutant (21.9 vs. 18.2 months; unstratified HR 0.72, 95% CI 0.37–1.39), and liver metastasis (NR vs. 20.2 months; unstratified HR 0.75, 95% CI 0.40–1.41) patients. The estimated OS rate at 2 years was 53.7% (95% CI 39.1–66.2), and 43.1% (95% CI 29.5–55.9) in group A, and group B, respectively. 38 (69.1%) patients in group A and 34 (59.6%) in group B had grade ≥3 treatment-related adverse events. Serplulimab/placebo-related deaths occurred in 2 (3.6%) patients in group A and 1 (1.8%) patient in group B. Conclusions: With an extended follow-up duration, improved survival benefits demonstrated with the addition of serplulimab were maintained in the first-line treatment of mCRC, alongside a manageable safety profile. These results support serplulimab plus HLX04 and XELOX as a promising first-line treatment option for mCRC that warrants further investigation. Clinical trial information: NCT04547166 .