Background: The determination of the pleural fluid (PF) carcinoembryonic antigen (CEA) concentration has proved helpful in the differentiation between pleural effusions (PE) of malignant and benign origin. The present study was designed to prospectively compare the utility of CEA with that of a recently introduced tumour marker, carbohydrate antigen 549 (CA 549).
Patients and methods: In 383 consecutive patients referred for thoracentesis (130 malignant and 253 benign), pleural and serum levels of CEA and CA 549 were, respectively, determined by enzyme immunoassay (EIA) and immunoradiometric assay (IRMA).
Results: CEA and CA 549 showed a high specificity for malignancy in serum (97 and 96%, respectively) and PF (98 and 99%). The serum sensitivity was 33% for CEA and 47% for CA 549 while in PF was 49 and 54%, respectively. The area under the curve of CA 549 (0.78) was significantly larger than that of CEA (0.66) in serum (P < 0.005) and in PF (0.83 and 0.75, respectively, P < 0.02) as well. CA 549 showed a higher sensitivity (P < 0.001) than CEA for ovarian tumours. In PF, the accuracy of the combination of both markers was higher than that of any individual marker, although the difference was only significant with respect to CEA (P < 0.02).
Conclusions: The results of the present study show that a new tumour marker CA 549 is at least similar in terms of sensitivity and specificity to CEA in the evaluation of patients with PE of unknown cause.