Prostatic acid phosphatase immunoperoxidase staining of cytologically positive effusions associated with adenocarcinomas of the prostate and neoplasms of undetermined origin.

An immunoperoxidase staining technique was employed in an effort to demonstrate prostatic acid phosphatase in sections of the effusion cell blocks in a retrospective investigation of the incidence of malignant prostatic cells in body cavity effusions in 33 patients with histologically confirmed prostatic cancer. An attempt was also made to identify the prostate as a possible anatomic site of origin in 26 patients with an unknown primary but with cytologically positive fluids. Neoplastic cells were identified in the effusion specimens in 21.2% of the patients with confirmed prostatic cancer; the sources, however, were either primary or metastatic carcinomas of nonprostatic origin. None of the cytologic specimens in this study demonstrated a positive prostate-specific acid phosphatase staining reaction, as did the prostatic metastases to the lungs used as controls.