[The study of pleural effusion supernatant cell-free tumor DNA in tumor mutational burden assessment of advanced lung cancer]

Objective: To evaluate the feasibility of cell-free tumor DNA in pleural effusion supernatant for assessing the tumor mutational burden (TMB) of advanced lung cancers. Methods: From December 2016 to August 2018, 34 lung cancer patients (19 males and 15 females) with pleural effusion were enrolled at Zhongshan Hospital, Fudan University. The median age of the patients was 65 (range, 34-85) years. Before systemic or local antitumor therapy, tumor specific mutations in tumor tissue, pleural effusion supernatant, pleural effusion sediment, and plasma samples from these patients were examined using targeted next-generation sequencing, and TMB levels were calculated respectively. Subgroup analysis was based on smoking history and driver mutation status. Statistical differences were determined using SPSS 16.0 software, and individual groups were compared using the one-way analysis of variance (ANOVA) and LSD-t test. Results: The median TMB level of pleural effusion supernatant was 6.23 mutations/Mb, similar to that of tumor tissue (6.23 vs 6.86 mutations/Mb, t=1.174, P=0.245), but significantly higher than that of pleural effusion sediment (2.49 mutations/Mb, t=3.044, P=0.003) and plasma (2.49 mutations/Mb, t=2.464, P=0.016). Compared with tumor tissue in TMB assessment, pleural effusion supernatant had a positive percentage agreement of 52% (9/17), and a negative percentage agreement of 65% (11/17). Subgroup analysis showed that the TMB level was higher in smokers (n=11) than that in non-smokers (n=23, 14.4 vs 5.4 mutations/Mb, t=3.238, P=0.003). Conclusion: For advanced lung cancer patients with pleural effusion, pleural effusion supernatant is a promising substitute to tumor tissue for TMB assessment, which is a potential biomarker for immunotherapy.