Mammaglobin (10 kD) is a breast-associated glycoprotein distantly related to secretoglobin family that includes human uteroglobin and lipophilin. Mammaglobin mRNA is present in high levels in human breast cancer cell lines, which has been shown to be a sensitive marker of breast cancer^1,2,3. When combined with other breast-restricted markers such as GCDFP-15, an overall sensitivity for breast carcinoma of 84% has been achieved⁴. Anti-Mammaglobin can also be used to determine breast origin in the setting of metastatic carcinoma^5,6.