HDAC9 and breast cancer: In this context, 17‐AAG displays strong antitumour efficacy in all three molecular subtypes of breast cancer cells, and sensitizes cancer cells to cytotoxic chemotherapeutic agents (such as taxol), radiation, and other targeted therapeutic agents such as HDAC inhibitors, mTOR inhibitor rapamycin and HER2‐targeting antibody trastuzumab.30, 46, 47, 48, 49