Tumor cells evade these checkpoints by genetic and epigenetic alterations to influence neoantigen formation, presentation, and/or processing, as well as alterations in cellular signaling pathways that disrupt the action of cytotoxic T cells.41 Identification of the PD-1/PD-L1 and CTLA4 pathways have provided opportunity for manipulation of these checkpoints to block the immune evasion by cancer cells. Here, CTLA4 is linked to neoplasm.