Clinical value of droplet digital polymerase chain reaction method in detecting plasma circulating tumor deoxyribonucleic acid epidermal growth factor receptor mutations in advanced pulmonary adenocarcinoma patients

Abstract

Objective: To determine the clinical value of droplet digital polymerase chain reaction (ddPCR) method to detect plasma circulating tumor DNA (ctDNA) epidermal growth factor receptor (EGFR) mutations in advanced pulmonary adenocarcinoma. Methods: One hundred and thirty six patients with advanced pulmonary adenocarcinoma diagnosed in the Beijing Chest Hospital were collected from May 2015 to April 2017 for initial treatment. EGFR gene mutation in the plasma ctDNA was detected by both ddPCR and amplification refractory mutation system (ARMS) assays. EGFR gene mutation in the tumor tissue was detected by ARMS assay. Patients with EGFR sensitive mutations received first-line oral treatment with EGFR tyrosine kinase inhibitor (EGFR-TKI) drugs. The Kaplan-Meier survival analysis was used to compared the progression-free survival (PFS) in EGFR gene mutated patients detected with different methods. Results: Total of 111 samples (81.6%) were detected with EGFR gene mutations in 136 tumor tissue samples. In the 111 samples, 48 samples were found with exon21 L858R mutation (48/111, 43.2%), 59 samples were found with exon19 deletion mutations (59/111, 53.2%), and 4 cases were found with other mutations (4/111, 3.6%). Using tumor specimens as the gold standard, the sensitivity, specificity, and concordance rate of ARMS assay were 58.6%, 96.0%, and 65.4%, respectively; and those in ddPCR assay were 79.3%, 100%, and 83.1%, respectively; the coincidence rate was 83.1% (Kappa=0.685, P<0.001). Kaplan-Meier survival analysis showed that patients with EGFR gene mutation detected by both ddPCR and ARMS methods had shortest PFS when compared with those in patients detected positive with a single method of ddPCR or ARMS assay (11.6 moths vs 14.8 months, χ(2)=2.517, P=0.026). Conclusions: ddPCR is a reliable technology with high sensitivity and high specificity to detect EGFR gene mutations in plasma ctDNA in patients with advanced pulmonary adenocarcinoma. Plasma EGFR gene mutation may predict the efficacy of EGFR-TKI drugs.