Measurement of placental alkaline phosphatase activity in benign and malignant pleural effusions.

The usefulness of placental alkaline phosphatase (PLAP) as a diagnostic marker of malignancy was assessed in pleural fluid from 60 patients with effusions. Pleural fluid PLAP activities were measured by an enzyme linked immunoassay (ELISA) using the two monoclonal antibodies H17E2 and H317. Similar values were found in groups of patients with primary bronchial tumours (n = 12), secondary malignancies (n = 23), and "benign" conditions (n = 25). The highest values were found in a small subgroup of patients with metastatic ovarian carcinoma. However, the production of this enzyme by normal lung makes the measurement of PLAP in pleural fluid unhelpful as a diagnostic aid to distinguish "benign" from malignant effusions.