HDAC9 and triple-negative breast carcinoma: Reports have shown that inhibition of HDAC can reactivate the expression of functional ER in ER-negative breast cancer cells11 and re-sensitize the ER-negative breast cancer cells to tamoxifen (TAM), indicating that the combination with HDAC inhibitors will render antiestrogens-based endocrine therapy a new viable treatment for triple negative breast cancers (TNBCs)14, 15.