The goal of this clinical trial is to compare XELOX +Bev +Tislelizumab with standard chemotherapy，in MSS/pMMR-type RAS-mutated metastatic colorectal adenocarcinoma. The main questions it aims to answer are efficacy and safety of the regimen of XELOX +Bev +Tislelizumab. The investigators want to transform ras-mutated colorectal cancer into a "hot tumor" through the combination of anti-vascular therapy and chemotherapy, and then achieve better therapeutic effect through the combination with immunotherapy. Participants will receive the regimen of XELOX +Bev +Tislelizumab.
Histologically confirmed initially unresectable MSS/pMMR-type RAS-mutant metastatic colorectal adenocarcinoma;
ECOG score of 0 or 1;
Ability to swallow oral medications;
Have at least one measurable lesion (according to RECIST v1.1 standard);
Previously received bevacizumab or anti-CTLA4, anti-PD-1/PD-L1 therapeutic antibodies or pathway-targeted drugs;
Received radiotherapy within 4 weeks before the evaluation;
Symptomatic peripheral neuropathy > grade 2 (CTCAE5.0 standard);
Received live vaccine or systemic immune stimulant (including but not limited to interferon or interleukin 2) within 1 month;