Diagnosis of malignant ascites in prostate cancer by measurement of prostate specific antigen.

We were confronted with a case of ascites in a man with known cirrhosis and advanced prostate cancer. Initial studies of ascitic fluid suggested cirrhosis as the cause of ascites. However, a prostate-specific antigen (PSA) study of ascitic fluid strongly suggested that the ascites was caused by prostate cancer. Subsequent cytologic studies confirmed malignant ascites. We suggest that measurement of PSA may be a valuable adjunctive study for the diagnosis of malignant effusions in prostate cancer.