Effectiveness of erlotinib in lung adenocarcinomas with classic and alternative EGFR mutations detected by Roche 454 GS-FLX next-generation sequencing (NGS).

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e19090^ Background: Next generation sequencing (NGS) detects all possible mutations with a higher sensitivity than Sanger sequencing. EGFR mutations are important predictors of sensitivity and resistance to EGFR tyrosine kinase inhibitors including erlotinib. The clinical significance of alternative (“rare”) EGFR mutation types, and mutation present in a small fraction of tumor cells detected by NGS is less known. Methods: For the present retrospective analysis, 100 lung adenocarcinoma tumor samples were collected from patients who participated in a previous observational cohort study of erlotinib (MOTIVATE). In this study only patients with advanced (IIIb/IV) K-RAS wild type tumors refractory to one or two previous chemotherapy were enrolled. Four exons (18, 19, 20, 21) of EGFR gene were PCR amplified and sequenced by Roche 454 GS FLX sequencer. Differences in overall survival (OS), and progression free survival (PFS) were statistically analyzed (Log Rank). Results: 47 mutations of the EGFR tyrosine kinase domain were detected in the 35 out of 100 tumors. 14 mutations were present in less than 10% of alleles. 16 tumors contained known („classic”) sensitizing mutations: nine deletions in exon 19, five L858R, one L861Q mutation in exon 21, one G719A mutation in exon 18 and one known resistance mutation D770_N771insY in exon 20. 18 tumors contained only alternative mutations with unknown functional relevance. The median PFS of patients with tumors harbouring EGFR wild type gene, classic EGFR mutations and alternative mutations were 2.9 months, 13.2 months (p<0.001) and 3.0 months (P=0.43) respectively. The median OS of patients with tumors containing wild type EGFR tumors, and alternative mutations was 7.2 and 5.5 months respectively (P=0.68). The median OS of patients harbouring classic EGFR mutations was not reached. The mean OS of these patients was 29.0 months. Conclusions: NGS is a sensitive and reliable diagnostic method to detect EGFR mutations with known functional significance. Alternative mutations need further one by one functional interpretation and analytical validation before being used as positive predictors in clinical decisions.

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