HDAC9 and breast cancer: A recent study in a breast cancer cell line also showed that the promoter hypermethylation-mediated inactivation of the hMSH2 gene was associated with the acquired resistance against doxorubicin, and the demethylating agent 5-aza-dC and the HDAC inhibitor Trichostatin-A significantly re-sensitized resistant cells to doxorubicin [20].