Liquid biopsy for EGFR mutations in non-small cell lung cancer cases by RT-PCR

Introduction: About 80% of lung cancer cases are classified as “Non-Small Cell Lung Cancer (NSCLC)”. Case spesific, targeted therapies (precision medicine) are developed for advanced NSCLC. The main targets are the mutations of EGFR gene which are found in 10-30% of cases. Tyrosine kinase inhibitors (erlotinib, gefitinib, afatinib, osimertinib) are offered if the tumor has the mutations. At the 9-13th months of targeted tyrosine kinase therapy, drug resistance related EGFR T790M mutation may occur. Aim: Our goal is to identify the effect of liquid biopsy in the management of NSCLC and share the results of our genetic diagnosis center. Methods: We have examined 42 mutations of EGFR gene, in 114 NSCLC cases that referred to our center in 2017-2018. Plasma derived cell-free DNA (cfDNA) samples are used to identify 42 mutations of EGFR gene including exon 19 (Ex19del), exon 20 (T790M), exon 21 (L858R) variants by “Real-Time Quantitative PCR” (RT-PCR) method. Results: The EGFR mutations are found in 23 liquid biopsy cases (20%). Eleven of the cases (9.6%) have single sensitivity related mutation: Five cases have Ex19del, 4 cases have L858R, 2 cases have Ex20ins. In addition, one case has “Ex19del and G719X” together. The remaining 11 (9.6%) have the drug resistance related T790M mutation in addition to a sensitivity mutation: Six cases have “Ex19del ve T790M”, 4 cases have “L858R ve T790M”, 1 case has “L858R, S768I ve T790M”. The 11 cases with normal liquid biopsy result actually have a EGFR mutation in solid tissue biopsy. Conclusion: The liquid biopsy is successfully took its place in the identification of EGFR mutations of advanced NSCLC cases.