MSI colorectal cancers (CRCs) comprise approximately 15 % of the total sporadic CRCs, and these tumors have been shown to upregulate expression of immune checkpoints including PD-1, PD-L1, CTLA-4, LAG-3, and IDO in tumor infiltrating lymphocytes (TILs), stroma or tumor invasive front compartments [11]. This evidence concerns the gene IDO1 and neoplasm.