Histone deacetylase inhibitors (HDACIs), as an important class of antitumor drugs, were capable of either altering gene transcription or inhibiting HDAC activity, thereby affecting the cell growth inhibition, differentiation, apoptosis, and tumor angiogenesis.44–46 Previous studies have shown that HDACIs not only induce histone H3 hyperacetylation (Ac-histone H3), but also up-regulate the expression of the p21 gene.47 Thus, the expressions of Ac-histone H3 and p21 proteins in MDA-MB-231 cells were evaluated by western blot assay. This evidence concerns the gene HDAC9 and neoplasm.