Mammaglobin, 10 kDa, is a cytoplasmic protein, a mammary-specific member of the uteroglobin family. It is related to a family of epithelial secretory proteins including prostatein and Clara cell protein. Mammaglobin occurs in about 80% of breast carcinomas. The extent is generally larger than that of GCDFP-15. Up to 15% of nonbreast carcinomas (such as stomach, lung, colon, hepatobiliary, thyroid, ovarian, and urothelial carcinomas) have been reported positive, usually only focally. Mammaglobin is a sensitive and fairly specific marker for breast carcinoma. The panel should also include Gross cystic disease fluid protein-15 and Estrogen receptor alpha.