Malignant pleural effusions for cancer genotyping: A matter of trans-pleural traffic of cell-free tumor DNA

Body cavity fluids accumulating in progressive malignancies are potential subjects of regular clinical testing for cancer-related features. Besides the cellular component, the supernatant of the fluid proved to gain diagnostic impact as the cell-free DNA (cfDNA) fraction ideally reflects general molecular features of the related tumorous process, e.g. in lung carcinoma. Thus, malignant pleural effusions can be used for lung cancer genetic profiling and this might remain the only source for testing in critical cases. The cfDNA concentration of the pleural effusion depends on many factors in both benign and malignant conditions. Further to direct pleural metastatic spread, the redirection of tissue lymphatic circulation, tumor angiogenesis, inflammatory processes and other variables may contribute to or enhance the enrichment of the effusion tumor DNA from the earliest stages of carcinogenesis. Our review addresses the traffic of cfDNA in the pleural space and the diagnostic utility of effusion cfDNA from the perspective of the complex pleural pathophysiology.