Abstract 1867: Characterization of multiple driver alterations in acquired resistance to osimertinib in EGFR-mutated lung cancer: implementation of single cell approaches

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Abstract Background Despite a primary benefit, resistance to the 3rd generation EGFR-Tyrosine Kinase Inhibitor (TKI) osimertinib invariably occurs. Several reports have recently highlighted the emergence of new oncogenic alterations as an actionable mechanism of resistance. However, the question of whether those alterations occur within a single tumor cell or in distinct tumor cell populations is still pending. Understanding those mechanisms at a cellular level is essential for a better comprehension of acquired resistance mechanisms and to identify new therapeutic opportunities. Methods This project studied tissues and patient derived cell lines from the ongoing prospective MATCH-R study (NCT0251782), in which patients with unresectable or metastatic cancer are included upon acquired resistance to targeted therapies or immunotherapy. Serial blood samples and tumor biopsies are collected at progression, for targeted NGS, WES and RNAseq, as well as PDX and patient-derived cell lines development. EGFR-mutated patients presenting a new driver alteration at osimertinib progression were identified. Single cell isolation and whole genome amplification were performed on corresponding frozen biopsies and derived cell lines. Cell lines were then exposed to specific inhibitors targeting the different pathways involved and functional analysis were performed to study the efficiency of combining different targeted therapies. Results Out of 466 patients included in MATCH-R study since June 2015, 110 patients presented EGFR-mutated adenocarcinoma. Among the 38 patients who experienced progression to 2nd line osimertinib, 5 patients were identified with a new oncogenic driver alteration, including STRN-ALK fusion (n=1), FGFR3-TACC3 fusion (n=1), BRAFV600E mutation (n=2), KIF-RET fusion (n=1). One patient progressing to 1st line osimertinib was identified with FGFR3-TACC3 fusion. All samples presented the persistence of EGFR activating mutation, i.e. EGFR exon 19 deletion (n=4) and exon 21 L858R mutation (n=2). After single cell isolation from tissue biopsies, PCR and targeted NGS allowed to highlight the co-existence of both drivers within single tumor cells for three patients. The remaining samples are still under investigation. Combination strategies with dual TKI are currently ongoing in order to restore sensitivity in cell lines (IC50 and Western Blots). Perspectives These data allow a better understanding of mechanisms underlying cell adaptation to EGFR-driven tumor inhibition. Combining targeted therapies represents a valuable therapeutic opportunity to overcome drug resistance in EGFR-mutated lung cancer. Updated results will be presented at the Meeting. Citation Format: Jeanne Chen, Floriane Braye, Francesco Facchinetti, Ludovic Lacroix, Jean-Yves Scoazec, Lambros Tselikas, David Planchard, Laura Mezquita, Anas Gazzah, Charles Naltet, Pernelle Lavaud, Aline Maillard, Stefan Michiels, Christophe Massard, Ken.A. Olaussen, Fabrice André, Gilles Vassal, Jean-Charles Soria, Benjamin Besse, Luc Friboulet. Characterization of multiple driver alterations in acquired resistance to osimertinib in EGFR-mutated lung cancer: implementation of single cell approaches [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1867.