CTLA4 and melanoma: However, most patients develop severe resistance to the drug after long-term administration.27 After the successful application of PD-1/PD-L1-based immunotherapy in melanoma and lung cancer treatment, the development of immunotherapy for the treatment of CRC has aroused wide concern.9,13 However, the success of PD-1 inhibitors or CTLA-4 inhibitors is limited to only some subtypes of CRC.