HDAC9 and breast cancer: Finally, HDAC isoenzymes 1, 2, and 3 are differentially expressed in BC: HDAC1 is highly expressed in hormone receptor positive BCs, correlates with better overall survival, and promotes proliferation of BC cells via activation of Snail/IL-8 signaling [145,146]; HDAC2 is highly expressed in hormone receptor negative BCs and correlates with tumor grade, lymph node status, and poor prognosis, as well as with several DNA-damage response genes [147]; HDAC3 also correlates with negative hormone receptor status and modulates apoptosis, cell cycle, metastasis, and angiogenesis [148].