Comparative cell-free mutation analysis for diagnosis of malignant pleural effusion in lung cancer patients

<bold>Introduction:</bold> Malignant pleural effusion (MPE) in lung cancer patients (LCP) reduces treatment efficacy and quality of life. However, pleurocentesis may not reliably identify MPE. The aim of this prospective observational study was to assess whether cell-free mutation analysis of unclear PE in LCP helped identify MPE based on identical mutation patterns. <bold>Methods:</bold> LCP (N = 17, 47% women) with PE underwent pleurocentesis. PE and blood plasma was transferred to cell-free DNA stabilising blood collection tubes. Genomic DNA was extracted and targeted next generation sequencing mutation analysis was performed using a customised DNA panel that covers coding regions of 40 genes. Transudative PE due to heart failure served as a tumour-free negative control (NC, N=3). <bold>Results:</bold> LCP had advanced tumour stage (88% stage IV; 76% adenocarcinoma). The most prevalent mutations in PE, tumour, and plasma were <italic>TP53</italic> (76%, 71%, 47%, respectively) and <italic>KRAS</italic> (24%, 35%, 29%, respectively). In 17 LCP, 25 mutations were detected in tumour, 23 mutations in PE (92% of tumour mutations) and 17 mutations in plasma. Comparing PE with tumour or plasma, identical mutations occured in 9/17 or 13/17 LCP, respectively. In 10/17 LCP, PE was cytopathologically tumour-free, but still contained 86% of the tumour-specific mutations. In 7/10 PE, we detected identical mutation patterns compared to tumour, suggesting MPE. In 4/17 LCP, cell-free tumour mutation analysis in PE was superior to plasma. In NC, no mutations were found in PE. <bold>Conclusion:</bold> Comparative cell-free mutation analysis of tumour, PE and blood helped identify MPE, even before cytopathological proof. This can improve therapeutic decision making in daily routine practice.