Quantification of plasma EGFR mutations in patients with lung cancers: Comparison of the performance of ARMS-Plus and droplet digital PCR

Objectives: EGFR mutation is a key factor to predict EGFR-TKI efficacy. However, a significant number of advanced patients do not have sufficient tumor specimens for molecular testing. Also, there is a lack of quantitative assay to analyze the mutant abundance. This study aims to evaluate the detection efficiency and clinical feasibility of a new platform, namely ARMS-Plus, for the detection and quantification of EGFR mutations in plasma. Materials and methods: The detection limit of ARMS-Plus was assessed by detecting spiked mutant plasmids which were serially diluted with normal human genomic DNA. The cutoff values were defined by examining the mutant copy numbers presented in 134 healthy controls. Plasma samples from 65 lung cancer patients were collected to evaluate the clinical performance of ARMS-Plus. EGFR mutations were concurrently tested by droplet digital PCR (ddPCR) for the plasma samples and conventional amplification refractory mutation system-PCR (ARMS-PCR) for the matched tumor tissue specimens to serve as a standard for comparison. Results: In this study, the analytical sensitivity of ARMS-Plus was 0.015%. The cutoff values of EGFR 19Del, L858R, T790 M mutations were defined as 2, 5, and 3 copies/mL, respectively. With tumor specimens as the standard, the sensitivity, specificity, and concordance rate of ARMS-Plus and ddPCR were 60.7%, 94.6%, and 80.0%; and 50.0%, 97.3%, and 76.9%, respectively. For quantification, the plasma 19Del and L858R mutant abundance detected by ARMS-Plus and ddPCR were consistent (Spearman R = 0.7956 and 0.7710, P< 0.0001). Conclusion: ARMS-Plus is a reliable, convenient and cost-effective method for the detection and quantification of plasma EGFR mutations.