HDAC5 and breast cancer: Because HDAC2 and HDAC5 positively regulate the expression of survivin and negatively regulate the expression of miR-125a-5p in ER+ breast cancer cells, targeting HDAC2 and HDAC5, or their downstream regulating molecules like survivin and miR-125a-5p, may be a potential strategy for overcoming resistance to hormone therapy in patients with ER+ breast cancer.