Abstract Rationale The management of lung cancer related malignant pleural effusions (MPE) depends on accurate molecular profiling to guide systemic treatments. Currently, this is only attempted on cell pellets containing a minimum requirement of detectable malignant cells. However up to 40-60% of MPEs are cytologically negative (CNMPE), leaving many patients requiring further invasive procedures to obtain adequate tissue for testing. This study investigates the feasibility of sequencing routinely discarded pleural fluid supernatant, which contains cell-free DNA (cfDNA), as an alternative source for molecular profiling. Methods We prospectively recruited all individuals with lung cancer related effusions presenting to Beaumont Hospital, Dublin, Ireland over a 15 month period. Matched serum and pleural fluid samples were collected for each participant. cfDNA levels were quantified and a targeted next generation sequencing (NGS) panel was performed on matched plasma and pleural supernatant samples post centrifugation. Molecular findings were compared with clinically obtained tissue results where available. Results Twenty-six individuals were recruited: 16 with MPE, 8 with CNMPE and 2 with paramalignant effusions. Median cfDNA concentrations in plasma were similar across the three groups—1.87 ng/µL (0.79-3.59) and 2.19 ng/µL (0.59-8.6), respectively (p = 0.743). Figure 1A The median concentration of cfDNA in the pleural supernatant of the three groups was also similar, 2.19 ng/uL (0.85,16.1), 2.12 ng/uL (0.40-8.420) and 2.51 ng/uL (1.46-3.56) respectively (p = 0.688). Figure 1B No correlation was observed between total pleural cfDNA concentration and variant allele frequency(rho=0.02, p = 0.61). The breakdown of effusion types, histological diagnosis, and somatic mutations detected in pleural supernatant are outlined in Figure 1C. Across the entire cohort, plasma and pleural supernatant detected a similar median number of mutations per individual, 2 (0.75-4) and 1 (0-2.25) (p = 0.189). However in those with MPE more somatic mutations were detected in pleural supernatant compared to plasma, 3 (1.5-3) vs 1 (0-2.5), (p = 0.0432) and at a higher allele frequency 16.1% (1.8%-27.8%) vs 1.8% (1.3%-15.5%), (p = 0.034). Notably, lung cancer-related somatic mutations were detected in 4 of 6 (67%) individuals with CNMPE, none of whom had sufficient material for tissue-based NGS. Figure 1C Conclusion This exploratory study suggests that the sequencing of cfDNA from discarded pleural fluid supernatant is a potentially viable option for molecular profiling in both those with MPE and CNMPE. Incorporating pleural supernatant analysis into routine workflows could reduce the need for further invasive procedures and expedite the time to treatment decision in those with lung cancer related effusions This abstract is funded by: StAR MD programme, CHEST
Ridge et al. (Fri,) studied this question.