IDO1 and neoplasm: The immunosuppressive TME in CM is composed of different immune cells, such as FoxP3+ Regulatory T cells (Tregs) and tumor-associated macrophages (TAMs), by the expression of immunomodulatory proteins, of which programmed death ligand 1 (PD-L1) and indoleamine 2,3-dioxygenase (IDO) are notable examples, as well as different immunomodulatory cytokines and fibroblasts [4].