Detection of epidermal growth factor receptor mutations in exhaled breath condensate using droplet digital polymerase chain reaction

The detection of certain oncogenic driver mutations, including those of epidermal growth factor receptor (EGFR), is essential for determining treatment strategies for advanced non-small cell lung cancer (NSCLC). The current study assessed the feasibility of testing exhaled breath condensate (EBC) for EGFR mutations by droplet digital PCR (ddPCR). Samples were collected from 12 patients with NSCLC harboring EGFR mutations that were admitted to Okayama University Hospital between June 1, 2014 and December 31, 2017. A total of 21 EBC samples were collected using the RTube™ method and EGFR mutations (L858R, exon 19 deletions or T790M) were assessed through ddPCR analysis (EBC-ddPCR). A total of 3 healthy volunteer samples were also tested to determine a threshold value for each mutation. Various patient characteristics were determined, including sex (3 males and 9 females), age (range 54-81 years; median, 66 years), smoking history (10 had never smoked; 2 were former smokers), histology (12 patients exhibited adenocarcinoma), clinical stage (9 patients were stage IV; 3 exhibited post-operative recurrence) and EGFR mutation type (4 had L858R; 8 had exon 19 deletions; 8 had T790M). EBC-ddPCR demonstrated positive droplets in 8 of the 12 patients. The sensitivity and specificity of each mutation was as follows: 27.3 and 80.0% for EGFR L858R, 30.0 and 90.9% for EGFR Ex19del, and 22.2 and 100% for EGFR T790M. EBC-ddPCR analysis of EGFR mutations exhibited modest sensitivity and acceptable specificity. EBC-ddPCR is a minimally invasive and replicable procedure and may be a complementary method for EGFR testing in patients where blood or tissue sampling proves difficult.