However, a key aspect of tumor development involves cancers acquiring immune escape mechanisms, such as inducing or recruiting immunosuppressive cells (e.g., regulatory T cells, myeloid-derived suppressor cells, and tumor-associated macrophages) and increasing the expression of various immunosuppressive molecules (e.g., PD-1 and PD-L1) [189, 190]. This evidence concerns the gene PDCD1 and neoplasm.