Mutational spectrum of acquired resistance to reversible versus irreversible EGFR tyrosine kinase inhibitors

Background: Mutational spectrum of acquired resistance to reversible versus irreversible EGFR tyrosine kinase inhibitors Over the past years, EGFR tyrosine kinase inhibitors (TKI) revolutionized treatment response. 1st-generation (reversible) EGFR TKI later the 2nd –generation irreversible EGFR TKI Afatinib was aimed to improve treatment response. Nevertheless, diverse resistance mechanisms develop within the first year of therapy. Here, we evaluate the prevalence of acquired resistance mechanisms towards reversible and irreversible EGFR TKI. Methods: Rebiopsies of patients after progression to EGFR TKI therapy (>6months) were targeted to histological and molecular analysis. Multiplexed targeted sequencing (NGS) was conducted to identify acquired resistance mutations (e.g. EGFR p.T790M). Further, Fluorescence in situ hybridisation (FISH) was applied to investigate the amplification status of bypass mechanisms like, MET or HER2. Results: 123 rebiopsy samples of patients that underwent firts-line EGFR TKI therapy (PFS >6months) were histologically and molecularly profiled upon clinical progression. The EGFR p.T790M mutation ist the major mechanism of acquired resistance in patients treated with reversible as well as irreversible EGFR TKI. Nevertheless a statistically significant difference for the acquisition of T790M mutation has been idientified: 45% of afatinib- vs 65% of reversible EGFR TKI treated patients developed a T790M mutation (p-value 0.02). Progression free survival (PFS) was comparable in patients treated with irreversible EGFR irrespective of the sensitising primary mutation or the acquisition of p.T790M. Conclusions: The EGFR p.T790M gatekeeper mutation ist he most prominent mechanism of resistance to reversible and irreversible EGFR TKI therapy. Nevertheless there is a statistically significant prevalence of p.T790M acquisition between the two types of TKI, which might be of importance for clinical therapy decision. Legal entity responsible for the study: The authors. Funding: Boehringer Ingelheim. Disclosure: S. Wagener-Ryczek: Honoraria: Boehringer Ingelheim. C. Heydt: Honoraria: AstraZeneca, BMS, Illumina. S. Michels: Honoraria: Novartis, Pfizer, AstraZeneca, Boehringer Ingelheim; Advisory roles: Boehringer Ingelheim, Pfizer; Research funding: Pfizer, Novartis, BMS; Travel support/accommodations: Novartis. J. Fassunke: Honoraria, advisory role: AstraZeneca. M. Tiemann: Honoraria: Pfizer, Novartis, Roche. L. Heukamp: Co-founder: Neo New Oncology. J. Wolf: Honoraria: AstraZeneca, BMS, Clovis Oncology, Lilly, MSD, Novartis, Pfizer, Roche; Advisory roles: AstraZeneca, BMS, Clovis Oncology, Lilly, MSD, Novartis, Pfizer, Roche, Amgen. R. Buettner: Co-founder, Chief Scientific Officer: Targos Molecular Pathology; Honoraria: Roche, Pfizer, Novartis, AstraZeneca, Qiagen, MSD, BMS, Lilly. S. Merkelbach-Bruse: Honoraria: AstraZeneca; Advisory roles: AstraZeneca, Roche. All other authors have declared no conflicts of interest.