CTLA4 and neoplasm: Immune checkpoint molecules—such as programmed cell death protein 1 (PD-1), its ligand PD-L1, cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), and T-cell immunoglobulin and mucin-domain containing-3 (TIM-3)—play pivotal roles in suppressing anti-tumor immunity (15).