Prostate marker immunoreactivity in salivary gland neoplasms. A rare pitfall in immunohistochemistry

A 66-year-old man presented with a mass just behind the lower part of the left ear. A biopsy showed a moderately differentiated adenocarcinoma that was prostate-specific antigen (PSA)- and prostate-specific acid phosphatase (PSAP)-positive. This finding suggested a metastasis of a prostatic carcinoma. Extensive clinical and radiographical examination revealed no primary prostatic carcinoma or other metastases and serum levels of PSAP and PSA were not elevated. The reliability of the PSA and PSAP staining was studied in a series of 25 adenocarcinomas of various primary sites in females and in 26 salivary gland tumors in both males and females, because a primary adenocarcinoma of salivary gland seemed another possibility in this case. As expected, there was no immunoreactivity for PSA and PSAP in the adenocarcinomas from females, but 6 of 11 pleomorphic adenomas, 0 of 4 monomorphic adenomas, 1 of 6 mucoepidermoid carcinomas, and 1 of 2 adenocarcinomas not otherwise specified (NOS) of the salivary gland showed at least focal staining of both PSA and PSAP. The conclusion was that the patient had a primary salivary gland adenocarcinoma NOS. In males with PSA- and PSAP-positive adenocarcinoma without signs of primary prostatic carcinoma, a salivary gland origin should be considered.