First, DNA methyltransferase and HDAC inhibitors (including 5-azacitidine (Vidaza), 5-aza-2′-deoxyazacytidine (decitabine)) can inhibit MDSCs with much lower doses than required for suppressing tumor cells within the TME, representing a better treatment for patients with high MDSC population in the TME [20,77]. Here, HDAC9 is linked to neoplasm.