TIGIT and neoplasm: Inhibitory immune checkpoint (iICPs) and their ligands such as T-cell immunoglobulin and mucin-domain containing-3 (TIM-3), programmed cell death-1 (PD-1), cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), lymphocyte-activation gene- 3 (LAG-3), B and T lymphocyte attenuator (BTLA), and T cell immunoglobulin and ITIM domain (TIGIT) are molecules expressed on the surface of cellular components in the TME, resulting in the suppression of anti-tumor immune responses and eventually leading to tumor survival and progression (18–20).