SRD5A1, a member of the steroid 5α-reductase family (SRD5A1, SRD5A2, and SRD5A3) converting testosterone to dihydrotestosterone (DHT), was recently reported to be aberrantly expressed in several sex hormone-related cancers, such as breast cancer, endometrial cancer, and prostate cancer4–6. The gene discussed is SRD5A1; the disease is breast cancer.