Sintilimab (IBI308) Combined With Bevacizumab + XELOX Regimen in Metastatic Colorectal Cancer

Inclusion Criteria: 1. Male or female, age ≥ 18 years old, ≤ 75 years old; 2. Metastatic colorectal adenocarcinoma confirmed by histology and unresectable metastatic colorectal cancer confirmed by a multidisciplinary team; 3. RAS gene mutation, BRAF wild-type and microsatellite stable confirmed by polymerase chain reaction using a panel of six mononucleotide repeat markers (BAT-25, BAT-26, NR-21, NR-24, NR-27, and MONO-27); 4. ECOG performance status of 0-1; 5. Life expectancy≥3 months; 6. Adequate organ and bone marrow functions: absolute neutrophil count \>1.5×109/L, hemoglobin \>8 g/dL, platelet count \>100×109/L, prothrombin time \<1.5 upper limit of normal (ULN), activated partial thromboplastin time \<1.5 ULN, bilirubin ≤1.5×ULN (could be extended to 3×ULN in case of liver metastasis), blood aspartate aminotransferase and alanine aminotransferase ≤2.5×ULN (could be extended to 5×ULN in case of liver metastasis), serum creatinine level ≤1.5×ULN or creatinine clearance ≥50 mL/min, urinary protein / creatinine ratio \< 1 (or urine analysis \< 1 + or 24-hour urinary protein \< 1g / 24 h; 7. Informed consent has been signed; 8. The presence of at least one measurable lesion assessed according to the Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1; Exclusion Criteria: 1. received previous treatment with any anti-programmed cell death protein 1 (PD-1) or anti-PD-L1 antibody; 2. received treatment with corticosteroids or other immunosuppressive agents within 14 days prior to study drug administration; 3. presence of autoimmune disease, known interstitial lung disease; 4. those with previous or concurrent malignancies expect for basal cell carcinoma, cutaneous squamous cell carcinoma, or cervical carcinoma in situ that have undergone radical treatment.