Droplet digital PCR improved the EGFR mutation diagnosis with pleural fluid samples in non-small-cell lung cancer patients

Background: Droplet digital polymerase chain reaction (ddPCR) is a promising method for analyzing minor amounts of nucleic acid. However, its application has not been reported in pleural fluid, which is an ideal sample source for epidermal growth factor receptor (EGFR) mutation analysis in non-small-cell lung cancer (NSCLC) patients. Methods: The extracted DNA from supernatants of pleural fluid was selected from our sample bank and re-analyzed by our previously established ddPCR assay. The results were compared with the former outcomes detected by direct sequencing or the amplification-refractory mutation system (ARMS). Results: A total of 95 samples were selected, and 64 and 31 of them had been performed with direct sequencing and ARMS tests, respectively. The EGFR mutation detection rate of ddPCR was significantly elevated, compared with both direct sequencing (75.4% vs. 43.8%, P < 0.0001) and ARMS (61.3% vs. 38.7%, P = 0.016). Compared with ARMS, Fisher's exact test showed that EGFR-positive patients who were redefined by ddPCR had higher objective response rates (ORRs): 57.9% vs. 16.7%, P = 0.032. Compared with direct sequencing results, Kaplan-Meier curves demonstrated that EGFR-positive patients who were redefined by ddPCR had longer progression-free survival (PFS): 8.0 vs. 2.0 months, P = 0.0001. Conclusion: We have demonstrated the clinical value of ddPCR in pleural fluid samples. The experience obtained from the present study is practical and favorable for the proper application of this new assay.