HDAC4 and breast cancer: To investigate how HDACs are targeted by panobinostat in BC, endogenous levels of HDAC proteins, including class I (HDAC1, HDAC2 and HDAC3) and class II (HDAC4, HDAC5 and HDAC6) HDACs, were first measured in BFTC909, UMUC-3 and T24 cells.