HDAC1 and breast cancer: This suggestion is consistent with one review paper, revealing that class I HDACs including HDAC1, HDAC2 and HDAC3 generally induce cell proliferation in cancer cells.23 According to a study published in 2016, HDAC5 expression was increased in human breast cancer, and HDAC5 was found to promote cancer cell proliferation.24 HDAC4 and HDAC5 have a reported similarity in amino acid sequences of 62%.25 CaMKII phosphorylates HDAC4 but not HDAC5.