Zhai K, et al. - The diagnostic utility of carcinoembryonic antigen (CEA) as well as carbohydrate antigen (CA) 15-3, CA 19-9 and CA 125 to distinguish malignant pleural effusion (MPE) and benign pleural effusion (BPE) was assessed in this derivation and validation study conducted in China. Findings showed that reliability displayed by CEA and CA 15-3 for differentiating MPE from BPE was found to be greater than that demonstrated by CA 125 and CA 19-9. In addition, it was observed that the sensitivity and specificity of the diagnosis etiology of pleural effusion (PE) may be improved with the use of the Δ(PE–serum) value in tumor markers, such as CEA and CA 15-3.