Tislelizumab Combined With Fruquintinib for Metastatic pMMR/MSS Colorectal Cancer

Inclusion Criteria: * 18-80 years old (including 18 and 80); * Histologically confirmed colorectal adenocarcinoma and biopsy pathology confirmed MSS/pMMR; * Gene testing confirmed ARID1A gene mutation (nonsynonymous); * No signs of intestinal obstruction; Or intestinal obstruction has been relieved after proximal colostomy; * Has received and failed ≥ 2 line of chemotherapy or progressed on or intolerable to oxaliplatin, irinotecan and fluorouracil chemotherapy after diagnosed with mCRC; * ECOG PS 0-2; * Able to swallow tablets; * Life expectancy of greater than 3 months; * Adequate bone marrow and organ function; * If female and of childbearing potential, must: * Have a negative pregnancy test ≤14 days prior to initiating study treatment * Agree to avoid pregnancy during and for 3 months after study treatment If male with a partner of childbearing potential, must: * Agree to use adequate, medically approved, contraceptive precautions during and for 3 months after the last dose of study treatment. * Able and willing to provide written informed consent for the study. Exclusion Criteria: * Any active autoimmune disease or history of autoimmune disease; * Those who are using immunosuppressive agents, or systemic or absorbable local hormone therapy to achieve immunosuppressive purpose, and continue to use within 2 weeks before enrollment; * Severe allergic reaction to other monoclonal antibodies; * Subjects with clinical symptoms of untreated active brain metastasis or meningeal metastasis; * Have received other PD-1 antibody therapy or other immunotherapy targeting PD-1/PD-L1 in the past; * Patients with high TMB (≥ 30Muts/Mb) and germline or somatic POLE/POLD1 gene mutations in the exonuclease domain; * There are clinical symptoms or diseases of heart that are not well controlled, such as: (a) heart failure of NYHA level 2 or above (b) unstable angina pectoris (c) myocardial infarction occurred within 1 year (d) clinically significant supraventricular or ventricular arrhythmia needs treatment or intervention; * Known hereditary or acquired bleeding and thrombophilia or being treated with thrombolysis or anticoagulation; * Urinary protein ≥ ++, or the 24-hour urine protein quantification greater than 1.0g; * Clinically significant bleeding symptoms or clear bleeding tendency within 3 months before enrollment; * Subjects with active infection; * Congenital or acquired immune deficiency (such as HIV infected persons), or active hepatitis (hepatitis B: HBsAg positive and HBV DNA ≥ 10\^4 copies/ml; hepatitis C: HCV antibody positive); * Other advanced malignant tumors within 5 years (except cured skin basal cell carcinoma, cervical carcinoma in situ, ovarian cancer, thyroid cancer and breast cancer); * Live vaccine may be inoculated less than 4 weeks before the study medication or during the study period; * Known or suspected to be allergic to the study drug or to any drug given in this trial; * Have any other disease, metabolic disorder, physical examination anomaly, abnormal laboratory result, or any other conditions that makes the subject not eligible according to the judgment of the investigator.