• 1\. Voluntarily sign a written ICF. 2. Age at enrollment: ≥ 18 years old, ≤ 75 years old, both male and female. 3. The Eastern Cancer Collaborative Organization (ECOG) has a physical fitness score of 0 or 1.

• 4\. The expected survival period is ≥ 3 months. 5. Metastatic colorectal adenocarcinoma confirmed by histology or cytology. 6. Microsatellite instability (MSI) status is MSI-L or MSS type human. 7. The metastatic lesion cannot be removed and is not suitable for curative surgical treatment.

• 8\. Previously only received first-line systemic anti-tumor therapy based on oxaliplatin (FOLFOX or CAPOX), and other systemic anti-tumor treatments for metastatic colorectal cancer are not allowed. Note: For subjects who have previously received neoadjuvant therapy, adjuvant therapy, or curative radiotherapy and chemotherapy, if disease progression occurs during or within 6 months after treatment, it is considered that they have received first-line treatment.

⁃ According to RECIST v1.1, subjects must have at least one measurable lesion. For subjects who have previously received radiotherapy, if there are no other lesions that can be selected as target lesions and there is objective evidence of significant progression after radiotherapy, the irradiated lesions can be considered as target lesions.

⁃ 10\. The subjects are required to provide 15 recently archived or freshly obtained FFPE pathological sections of tumor tissue.

⁃ 11\. Determine good organ function through the following requirements:

⁃ a) Hematology (no use of any blood components or cell growth factor branches within 7 days prior to starting treatment)

⁃ Holding treatment:

⁃ i. Neutrophil absolute value ANC ≥ 1.5 × 109/L (1500/mm3); Ii. Platelet count ≥ 100 × 109/L (100000/mm3); Iii. Hemoglobin ≥ 90 g/L. b) Kidney: i. The calculated value of creatinine clearance rate \* (CrCl) is ≥ 50 mL/min

⁃ \*The Cockcroft Fault formula will be used to calculate CrCl (Cockcroft Fault formula) CrCl (mL/min)={(140- age) × Weight (kg) × F} /(SCr (mg/dL) × 72) F=1 for males; F=0.85 for women; SCr=serum creatinine. Ii Urinary protein ≤ 1+or 24-hour (h) urinary protein quantification\<1.0 g. c) Liver: i. Total serum bilirubin (TBil) ≤ 1.5 × ULN; For liver metastasis or evidence to confirm/suspect Subjects with Gilbert disease, TBil ≤ 3 × ULN Ii. AST and ALT ≤ 2.5 × ULN; For subjects with liver metastasis, AST and ALT ≤ 5 × ULN Iii. Serum albumin (ALB) ≥ 28 g/L d) Coagulation function: i. International Standardization Ratio