Regardless of origin and type [59], dMMR/MSI tumors are susceptible to immunotherapy owing to: (1) high TMB (2) high TIL in both tumor and tumor-adjacent tissues [59, 92] (3) upregulation of PD-1 and IFN-γ signatures (PD-L1, CTLA-4, LAG-3 and IDO) representing an adaptive resistance to the immunoreactive microenvironment induced by MSI [5, 6]. This evidence concerns the gene IDO1 and neoplasm.