Tumor markers determination in malignant pleural effusion: pearls and pitfalls

Serum and pleural fluid tumor markers are well-recognized auxiliary diagnostic tools for malignant pleural effusion (MPE). Here, we discuss some pearls and pitfalls regarding the role of tumor markers in MPE management. The following issues are discussed in this article: What is the appropriate clinical scenario for evaluating pleural tumor markers? Which tumor markers should be advocated for diagnosing MPE? Can extremely high levels of tumor markers be employed to establish a diagnosis of MPE? Does the serum-to-pleural fluid ratio of a tumor marker have the same diagnostic efficacy as the measurement of that marker alone in the pleural fluid? Can tumor markers be used to estimate the risk of specific cancers? What should be considered when interpreting the diagnostic accuracy of tumor markers? How should tumor marker studies be performed? We addressed these issues with published works, particularly systematic reviews and meta-analyses.