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In this report we describe a cDNA sequence, BS106, identified from Incyte Genomics LifeSeq Expressed Sequence Tag database. A multi-tissue mRNA expression array, northern blots, and RT-PCR assays demonstrate the expression of BS106 in mammary, salivary and prostate glands, but not in other tissue types. BS106 mRNA was detected in 90% of the breast tissues examined. The cDNA encodes a 90-amino acid protein characterized as a small, mucin-like protein based on amino acid composition, extensive O-linked glycosylation, and expression profile. BS106 protein was recombinantly expressed in human embryonic kidney 293 cells and the secreted product was purified from the culture media. Monoclonal antibodies were prepared and used for immunohistochemical analysis of early stage breast cancer. BS106 protein was detected in the vast majority of carcinomas (70-100%) and overexpressed in approximately 30% of the 22 specimens analyzed. BS106 protein was not detected in other solid tumor types including bladder carcinoma, colon carcinoma, endometrial carcinoma, gastric carcinoma, squamous cell lung carcinoma, adenocarcinoma of the lung, ovarian carcinoma, pancreatic and prostatic carcinoma.