Cytology of metastatic adenocarcinoma of the prostate in pleural effusions.

Malignant pleural effusions due to prostatic carcinoma are rare. We examined the cytologic and clinical presentations of 14 malignant pleural effusions caused by prostate cancer. These cases represented 2.3% of all positive pleural effusions at our institution. All patients (n = 10) had high grade, high stage tumors, including three with small cell anaplastic carcinoma. Three cases had clinically documented metastases to pleura, and in two cases, metastases were documented at autopsy. Most tumor cells had large nucleoli and were arranged in small, loosely cohesive groups. Fluids due to the small cell type of prostate carcinoma often contained a mixture of cells similar to those seen in small cell carcinoma of other sites such as the lung, as well as cells resembling the more typical type of prostate cancer. Prostatic specific antigen and prostatic acid phosphatase were positive in less than 50% of these malignant effusions. We conclude that prostatic carcinoma in pleural effusions occurs most commonly in high grade, high stage tumors and has a characteristic cytologic appearance. Negative staining for PSA and PAP does not rule out a prostatic source for malignant cells in effusions.