Updated survival results of BBCAPX-II: Sintilimab combined with bevacizumab and CapeOx as first-line treatment in patients with RAS-mutant, microsatellite stable, unresectable metastatic colorectal cancer.

3563 Background: Microsatellite stable (MSS) and RAS-mutant metastatic colorectal cancer (mCRC) patients are characterized by an immunosuppressive microenvironment and a low response rate to immunotherapy. Sintilimab plus bevacizumab and CapeOX (BBCAPX) has proved its efficacy and safety in above unresectable mCRC patients (Ying Yuan et al. ASCO 2023 and Xuefeng Fang et al. ASCO 2022). Here, we report updated survival results of this single arm, open-label, phase 2 trial. Methods: Eligible patients were aged 18 to 75 years with histologically confirmed unresectable metastatic colorectal adenocarcinoma by multidisciplinary team, and had RAS gene mutation and confirmed MSS status. All patients received treatment with sintilimab (200 mg, day 1) plus bevacizumab (7.5mg/kg, day 1) and oxaliplatin (135 mg/m2, day 1) and capecitabine (1g/m2, bid, day 1-14) of each 21-day cycle. The primary endpoint included objective response rate (ORR) and adverse events. Secondary endpoint was disease control rate (DCR) and progression-free survival (PFS). Results: From April 2021 to December 2021, 25 patients were enrolled. The ORR was 84% and the DCR was 100%. Six (24%) patients underwent surgical treatment and unexpectedly achieved no evidence of disease status. At the data cut-off day (January 26, 2024), the median PFS in the full analysis set was 17.9 months (95% CI, 8.84-27), and the median PFS in the per-protocol set was 9.79 months (95% CI, 6.44-24.3). Median PFS was 23.7 months (95% CI, 4.8-NA) in the patients with only liver metastasis and 11.5 months (95% CI, 4.83-24.3) in the patients with other metastasis. The PFS rate at 6 months was 84% (95% CI, 70.8-99.7). The PFS rate at 12 months was 56% (95% CI, 39.6-79.3). The most frequent grade 3 or 4 TRAEs were neutropenia (3/25) and increased alanine transaminase (2/25). No grade 5 adverse events occurred during the study. Conclusions: The combination of sintilimab plus bevacizumab and CapeOx showed promising antitumor activity and manageable toxicity in RAS-mutant, MSS, unresectable mCRC. Patients with liver metastases presented better prognosis compared other metastases. Furthermore, we are currently launching a phase III, randomized, open-label, multicentric clinical trial (NCT05171660) to further analyze the effects, safety, and prognostic biomarkers of this regimen. Clinical trial information: NCT04194359 . [Table: see text]