The infiltration of immunosuppressive cells (Figure 3) such as tumor-associated macrophages (TAMs), regulatory T cells (Tregs), and myeloid-derived suppressor cells (MDSCs); the secretion of immunosuppressive cytokines such as transforming growth factor β (TGF-β) and interleukin 10 (IL-10); and the expression of immune checkpoints such as programmed death-ligand 1 (PD-L1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) play vital roles in immune evasion in PDAC [67,68]. This evidence concerns the gene CTLA4 and neoplasm.