Akkermansia Probiotics Plus Anti-PD-1 Monoclonal Antibody in MSS/pMMR Advanced Colorectal Cancer

After enrollment, patients will receive anti-PD-1 monoclonal antibody + Tyrosine kinase inhibitor (TKI, e.g., regorafenib, fruquintinib) treatment or anti-PD-1 monoclonal antibody ± chemotherapy (etc., CAPEOX \[oxaliplatin+capecitabine \], XELIRI \[irinotecan+capecitabine \]) ± Bevacizumab treatment (anti-PD-1 monoclonal antibody, chemotherapy, and bevacizumab every 3 weeks, TKI every 4 weeks), along with daily continuous administration of Akkermansia probiotics (Songke, dose: 1 capsule/day, taken with breakfast), until disease progression, intolerable toxicity, or patient withdrawal from the study.