Mammaglobin-B also known as secretoglobin family 2A member 1 is a protein that in humans is encoded by the SCGB2A1 gene. SCGB2A1 expression is highly specific of mammary tissue, and has been used for identification and detection of disseminated breast cancer cells. May bind androgens and other steroids, may also bind estramustine, a chemotherapeutic agent used for prostate cancer. May be under transcriptional regulation of steroid hormones.