P3.02b-029 Primary Double EGFR Mutations T790M and Mutation in Exon 19 or 21 - Prevalence and Treatment Results in Slovakian NSCLC Patients: Topic: EGFR Biomarkers

Abstract

Primary EGFR dual mutations comprising T790M and exon 19 or 21 mutation (SM, sensitizing mutations) are rare when common diagnostic methods are used. There are limited data about the treatment results with EGFR-TKIs in this setting. Purpose of this study was to find out the prevalence of primary dual EGFR mutations T790M and SM in the Caucasian population of NSCLC patients in Slovakia, and to evaluate treatment results with EGFR-TKIs in these patients. Retrospective multicenter study. The databases of the molecular/genetic diagnostic centers were searched for patients with dual EGFR mutations T790M and SM. Data regarding patients were obtained from the databases of participating institutions and patient files. Descriptive statistics was used for data analysis. Altogether 3883 patients were tested for EGFR mutation from 2010 through 2015. Allele specific PCR was used in majority, high resolution melting analysis, Sanger sequencing and mutant-enriched PCR were also used. Double mutations T790M and SM were found in only six cases, i.e. the observed period prevalence was 0.15%. Patients’ characteristics and the treatment results are in the Table. PS was improved after two months of treatment in patients with initial PS over 1, and remained unchanged in those with PS 1. There were no unexpected AEs. The prevalence of the dual EGFR mutations T790M and SM is very low in Caucasian population in Slovakia when common testing methods are used. Treatment results seen in this study suggest good effectiveness of the first or second generation EGFR-TKIs even in NSCLC with primary dual T790M and SM mutations. The quantitative analysis of these mutations using the blood sample is available at present. It might be useful in decision making about the use of the first – second or the third generation EGFR-TKI, based on the prevailing mutation.