Liposomal Irinotecan

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.