Frequency of EGFR mutations in Greek non-small-cell lung cancer (NSCLC) patients.

Abstract

e21141 Background: NSCLC patients harboring activating somatic mutations within the tyrosine kinase (TK) domain of the epidermal growth factor receptor (EGFR) significantly benefit from EGFR targeted therapy. Treatment with the recently approved EGFR inhibitor IRESSA (gefitinib) leads to improved response and survival outcomes, therefore screening for EGFR mutations has entered routine clinical practice. Several clinico-pathological factors correlate with these mutations including gender, smoking history, and histology. The frequency of EGFR mutations is also ethnicity-dependent, wherein the incidence in Asian populations is ~30%, while in Caucasians (Whites) it is lower, ~ 15%. However, limited data is available on intra-ethnic differences throughout Europe. Aim: The aim of this study was to determine the frequency and spectrum of EGFR mutations in an unselected group of Greek NSCLC patients and investigate technical aspects of analysis. Methods: We set up High Resolution Melting Analysis (HRMA) assays to identify mutations in exons 18-21 of the EGFR gene and validated their analytical sensitivity by making serial dilutions of samples with known mutations and tumor cell content (TCC). A total of 698 NSCLC patients were screened with HRMA for somatic EGFR mutations in exons 18-21 and mutation status was verified by bi-directional sequencing. Pathological review was obtained for all samples and macro-dissection was used to ensure a %TCC of >75% in all possible cases. Results: The sensitivity of our HRM assays was found to be ≤1.5% Using HRMA and bi-directional sequencing a frequency of 19.05% was obtained; 105 x exon 19, 21 x exon 21, 6 x exon 20 and 1 x exon 18 . Conclusions: Applying a very sensitive mutation detection technique in a large cohort of unselected Greek NSCLC patients in routine diagnostic practice, we obtained an overall mutation frequency of 19.05%. This mutation frequency is similar to that found by the SLADB and EURTAC studies in European populations. Differences in sensitivity between techniques suggest that more than one technique should be advised in routine diagnostic practice.