First identified as an H3K4 demethylase, a specific DNA-binding protein and a potential downstream target of HER2/ERBB2. KDM5B promoted cell proliferation though transcriptional repressing tumor suppressor genes, luminal-high genes, specific microRNAs and contributed to poor survival. In some certain types of breast cancer like ER- or TNBC, KDM5B served as an anti-oncogenic player. The gene discussed is KDM5B; the disease is breast cancer.