ESR1 and breast cancer: Previously, Varga et al. [11], showed that plasma membrane Ca2+-ATPase isoform PMCA4b is induced in response to HDACi in ERα+ and HER2+ breast cancer cell lines such as MCF-7, but not in basal/triple negative breast cancer lines MDA-MB-231 and Hs578T where expression of this gene is already significantly elevated.