PDCD1 and breast cancer: The concomitant administration of DNA methyltransferase (DNMT) and histone deacetylase inhibitors (HDACi) augments the efficacy of anti-programmed death-1 (anti-PD-1) and anti-cytotoxic T-lymphocyte-associated protein 4 (anti-CTLA-4) therapies in colorectal cancer (CRC) and breast cancer (BC) models by reducing myeloid-derived suppressor cells (MDSCs) [354].