RESUMO
OBJECTIVE: To examine the properties of mesothelial cells by measuring pleural cancer antigen 125 (CA-125) levels in different types of benign and malignant pleural effusions. DESIGN: In this retrospective study, pleural fluid was collected from 326 patients; pleural CA-125 levels were measured using radioimmunoassay. Patients were classified into five groups according to the aetiology of pleural effusions: I) tuberculosis, II) malignant, III) pyogenic, IV) congestive heart failure, and V) hepatic hydrothorax. RESULTS: CA-125 levels were significantly higher in the malignant group than in all benign groups. There was no difference in pleural CA-125 levels between transudate and exudate benign aetiologies. Although pleural CA-125 levels were significantly higher in malignant than benign effusions, about one third of malignant pleural effusions had levels of <600 U/ml. Among malignancies, there were no significant differences in pleural CA-125 levels between histological types. CONCLUSION: CA-125 levels in benign pleural effusions may not be influenced by pleural inflammation or hydrostatic or oncotic pressure changes. Pleural CA-125 levels may not be influenced by the histological type of tumour in malignant pleural effusions, suggesting that mesothelial cell properties may not be altered by these factors in the pleural space.