Phase II - Treatment Regimen Exploration Stage:
1. Evaluate the safety and efficacy of the following three treatment regimens:
Liposomal irinotecan + 5-FU/LV + bevacizumab + Enlonstobart (Group A) Liposomal irinotecan + 5-FU/LV + bevacizumab (Group B) Irinotecan + 5-FU/LV + bevacizumab (Group C) 2. Provide a basis for selecting the treatment regimen for the confirmatory phase. 3. Explore the relationship between tumor tissue, stool, and blood biomarkers and efficacy and adverse reactions in liposomal irinotecan combination regimens versus irinotecan combination regimens.
Phase III - Efficacy Confirmation Stage:
Compare the efficacy and safety of liposomal irinotecan combination regimens versus irinotecan combination regimens in second-line treatment of metastatic colorectal cancer.
Aged ≥ 18 years old and ≤ 75 years old.
Histologically or cytologically confirmed metastatic colon or rectal adenocarcinoma;
Patients must have at least one measurable lesion according to RECIST 1.1 criteria.
Had received first-line treatment based on oxaliplatin.
Patients with a history of other malignancies within the past 5 years, except for cured carcinoma in situ or basal cell carcinoma of the skin.
Prior treatment with irinotecan or liposomal irinotecan-based chemotherapy, or prior treatment with immune checkpoint inhibitors (including but not limited to PD-1 inhibitors, PD-L1 inhibitors, and CTLA-4 inhibitors).
Patients with left-sided colorectal cancer, RAS/BRAF wild-type, who did not receive cetuximab in first-line therapy.
Patients with known mismatch repair dysfunction or microsatellite instability ;