Whereas treatments with the enhancer of zeste homolog 2 (EZH2) inhibitor GSK126 promoted the expansion of MDSCs, impairing antitumor immunity [159], entinostat, a class I histone deacetylase (HDAC) inhibitor, impaired MDSCs’ immunosuppressive functions, improving the anti-tumor effects of anti-PD-1 antibodies [160]. This evidence concerns the gene HDAC9 and neoplasm.