The immune escape is favored by the continuous exposure to antigens and potentiated by different elements within the TME, such as cells (Tregs, myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs) and natural killer (NK) cells), cytokines (γ-IFN, IL6, IL10 and TGF-β) and other soluble factors (Indoleamine-pyrrole 2,3-dioxygenase (IDO) and VEGF), and determines T-cells loss of function [109,110] (Figure 2). This evidence concerns the gene IDO1 and neoplasm.