Mammaglobin is a breast-associated glycoprotein distantly related to secretoglobin family that includes human uteroglobin and lipophilin. Unlike other secretoglobin family members, mammaglobin mRNA expression is breast specific, which has been shown to be a very sensitive marker of occult breast cancer cells in sentinel lymph nodes and peripheral blood. By paraffin immunohistochemistry, the overall sensitivity of mammaglobin for breast cancers was reported about 80%. When combined with other breast-restricted markers such as GCDFP-15, an overall sensitivity of 84% could be achieved. Mammaglobin can play a contributing role in the identification of primary sites of carcinomas presenting at metastatic sites.