Fibronectin is unsuitable as a tumor marker in pleural effusions.

We studied 75 patients with nonmalignant pleural effusions (50 with pneumopathy, 16 with pulmonary tuberculosis, and nine with congestive heart failure) and 33 patients with malignant pleural effusions. We selected 105 mg/L as the most suitable cutoff concentration of fibronectin for distinguishing between the two groups. We found high concentrations of fibronectin in 21 of the 33 patients with malignant pleural fluid but also in 37 of the 75 patients with nonmalignant pleural fluid. Evidently, measuring fibronectin in pleural fluid will not help in differentiating nonmalignant from malignant pleural fluids (diagnostic accuracy: 55%).