Use of cytokeratin fragments 19.1 and 19.21 (Cyfra 21-1) in the differentiation of malignant and benign pleural effusions

Background: Differentiation between malignant and benign pleural effusions is often difficult. Serum level of Cyfra 21-1, a marker of cytokeratin 19 fragments, has been used in the diagnosis and monitoring of epithelial tumours, especially bronchogenic carcinomas. Aim: This study is designed to establish the usefulness of effusion Cyfra 21-1 level in differentiating malignant from benign effusions. Methods: Forty-eight malignant effusion aspirates (proven by cytology or pleural biopsy) and 34 benign samples were compared. Cyfra 21-1 concentration was measured by a solid phase sandwich radioimmunoassay (Centocur(R), USA). Results: Cyfra 21-1 level was significantly higher in malignant effusions (geometric mean 123.6 ng/mL, 95% confidence interval [CI] 76.6-199.4) than in benign ones (geometric mean 14.3 ng/mL, 95% CI 8.5-23.9), p<0.00005. By Receiver Operating Characteristics curve analysis, the sensitivity is 77% for a specificity of 79% if the cut-off is set at 32 ng/mL. No significant difference was observed (p=0.1) in Cyfra 21-1 concentration between adenocarcinoma and mesothelioma effusions. Cyfra 21-1 level was not influenced by the effusion protein concentration (r=0.29), or by renal function as measured by serum creatinine (r=0.1). There was no significant difference between Cyfra 21-1 levels in benign exudate and transudate effusions, p=0.28. Conclusions: Cyfra 21-1 is a useful adjunct in the workup of effusions but should not replace conventional investigations as there is considerable overlap in levels between benign and malignant groups. It is unable to differentiate between subgroups of malignancies.