Most recently, entinostat has been shown to down-regulate the number and function of two key immunosuppressive cells, myeloid derived suppressor cells (MDSCs) and regulatory T-cells (Tregs), in the tumor microenvironment thereby enhancing the activity of immune checkpoint inhibition. To date, entinostat has been investigated alone or in combination in >900 patients with cancer in clinical studies, including >600 patients with solid tumors. Entinostat as a single agent has been studied in metastatic melanoma and in combination has been studied in metastatic non-small cell lung cancer (NSCLC), breast cancer, renal cell cancer, and colon cancer.