PSA immunoreactivity in a parotid oncocytoma: a diagnostic pitfall in discriminating primary parotid neoplasms from metastatic prostate cancer.

Prostate-specific antigen (PSA) is secreted by both normal and neoplastic acinar cells of the prostate gland, and the immunohistochemical detection of PSA is widely accepted as an excellent method for confirming the prostatic origin of metastatic tumor implants in men with prostate cancer. Less recognized is the observation that certain nonprostatic tissues and their neoplastic counterparts also secrete PSA. As one example, salivary gland ducts and certain salivary gland neoplasms have been reported to be immunoreactive for PSA. Potentially, this nonspecificity could be a diagnostic pitfall when using immunoperoxidase on fine-needle aspiration (FNA) biopsy specimens to differentiate metastatic prostate cancer from primary salivary gland tumors. We report on a case where strong PSA immunoreactivity of a parotid oncocytoma led to its confusion with metastatic prostate cancer.