Importantly, ectopic over-expression of survivin attenuated the cell viability reduction effect caused by HDAC2 siRNA in MCF7, MCF7-TamC3, and ZR-75-1 cells, confirming the pro-survival role of the HDAC2-mTOR-survivin signaling pathway in ER+ breast cancer cells (Figure 3D). This evidence concerns the gene ESR1 and breast cancer.