HDAC5 protein is expressed in lung, brain, myocardium, skeletal muscle, and placenta, and accumulating evidence indicates that it has variable expression and functions in different types of tumor: HDAC5 is overexpressed in breast cancer (19, 20), hepatocellular carcinoma (HCC) (21), lung cancer (22), pancreatic neuroendocrine cancer(pNET) (23) and colorectal cancer(CRC) (24). The gene discussed is HDAC5; the disease is breast cancer.