SALIVARY DUCT CARCINOMA SECRETING PROSTATE-SPECIFIC ANTIGEN

Prostate-specific antigen (PSA) is a 30 kDa glycoprotein serine protea se that shows high tissue specificity for prostatic tissue, both benig n 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 ca ncers have been reported in the literature. The authors present a case of salivary duct carcinoma associated with elevated serum levels of P SA. 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 mu g/L was measured and this correlates with levels of P SA associated with metastatic prostatic carcinoma. High performance li quid chromatography with a molecular sieve column characterized the se rum PSA into both free protein (approximately 20%) and protein bound t o alpha-1-antichymotrypsin (PSA-ACT)(approximately 80%). Molecular wri ghts of the free PSA and PSA-ACT subfractions were 27-31 kDa and 100-1 10 kDa, respectively.