Mammaglobin is a 93 amino acids protein with homology to other secretoglobin-uteroglobin family members, that was originally identified in studies of differentially expressed cDNAs from breast carcinoma cell lines. In normal tissue, mammaglobin mRNA is specifically expressed in breast and skin tissue. Mammaglobin expression has also been reported in a series of malignant and nonmalignant tissues derived from the female genital tract by RT-PCR. Expression of the mammaglobin gene and protein has been demonstrated in neoplastic breast tissues and in a subset of normal breast epithelial cells within the acini of type I and type II lobules and within the columnar cells of terminal ducts. Mammaglobin has been found in well-, moderately-, and poorly differentiated invasive ductal carcinomas by IHC and in metastatic- and occult- breast carcinomas by RT-PCR.