In this report, we describe a novel cDNA isolated from a primary human breast adenocarcinoma and differentially expressed in several breast carcinoma cell lines. The protein encoded by this cDNA, which we have named mammaglobin, is homologous to a family of secreted proteins that includes rat prostatic steroid-binding protein subunit C3, human Clara cell 10-kilodalton protein, and rabbit uteroglobin. Expression of the mammaglobin gene is restricted to the adult mammary gland. More significantly, in an analysis of 35 breast tumor biopsies, mammaglobin mRNA levels were increased at least 10-fold relative to normal breast tissue in 23% of cases. The breast-specific expression of this potentially secreted protein and its frequent overexpression in primary human breast tumors suggest that mammaglobin may be a novel marker for the management of breast cancer.

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This work was supported in part by American Cancer Society IRG Grant No. ACS-IRG36-37.

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