Salivary duct carcinoma secreting prostate-specific antigen.

Prostate-specific antigen (PSA) is a 30 kDa glycoprotein serine protease that shows high tissue specificity for prostatic tissue, both benign and malignant. However, recent reports have shown that a variety of normal and neoplastic tissue types express PSA immunohistochemically. In addition, rare instances of the secretion of PSA by nonprostatic cancers have been reported in the literature. The authors present a case of salivary duct carcinoma associated with elevated serum levels of PSA. Both the primary tumor and metastases stained positively with anti-PSA monoclonal antibodies, but were negative with antibodies directed against prostate-specific acid phosphatase. Elevated serum PSA levels were confirmed with three different immunoassay methods. A peak serum level of 140 micrograms/L was measured and this correlates with levels of PSA associated with metastatic prostatic carcinoma. High performance liquid chromatography with a molecular sieve column characterized the serum PSA into both free protein (approximately 20%) and protein bound to alpha-1-antichymotrypsin (PSA-ACT)(approximately 80%). Molecular weights of the free PSA and PSA-ACT subfractions were 27-31 kDa and 100-110 kDa, respectively.