RecruitingPhase 2Drug trialA Study to Explore the Third-line Treatment of Fruquintinib Combined With Serplulimab in Advanced Non-liver-limited Metastatic Colorectal Cancer: a Single-center, Phase 2 StudyThe aim of this clinical trial is to learn about efficacy of fruquintinib combined with serplulimab in patients with microsatellite stabilized mCRC who have failed standard therapy. The main purpose is to explore efficacy, safety and tolerability of the treatment. At the same time, the correlation between biomarkers (including ctDNA, TPS, CPS, tumor mutation burden, lymphocyte subpopulation, cytokines, TCR, intestinal microbes, etc.) and the efficacy and drug resistance mechanism will be analyzed, which could provide reference for determining the advantaged group.