Abstract B004: Revealing the mechanisms of acquired resistance to osimertinib from re-biopsy specimens in advanced non-small cell lung cancer with EGFR T790M mutation (LOGIK1607)

Abstract

Abstract Background: Although treatment with osimertinib confers survival benefits in the second-line treatment of epidermal growth factor receptor (EGFR)-mutated lung cancer with the EGFR T790M mutation, the mechanism of acquired resistance to osimertinib has not been well understood. Here, we planned a multicenter, prospective observational study in order to clarify the possible acquired resistance mechanisms to second-line treatment using osimertinib in Japanese non-small cell lung cancer patients. Methods: EGFR T790M positive advanced non-small cell lung cancer patients were included in this study. We excluded EGFR tyrosine kinase inhibitor naïve patients, patients whose EGFR T790M proved only by liquid biopsy, and patients whose tumor specimens were not adequate for targeted resequencing analysis. Re-biopsy was planned after the patient developed acquired resistance to osimertinib under written informed consent. Nucleic acids were extracted from formalin-fixed paraffin embedded tumor sections and targeted resequencing was performed using a panel consisting of 143 genes (Oncomine Comprehensive Assay, OCA, ThermoFisher Scientific, USA) in a CLIA-certified laboratory (SRL Inc., Japan), and then analyzed using IonReporter software (ThermoFisher Scientific, USA). Results: Between November 2016 and February 2019, 86 patients from 25 institutions were screened. Among 71 patients who were eligible, 31 patients were still on osimertinib and 33 patients developed acquired resistance. Among the 33 patients who developed acquired resistance, 16 patients proceeded to re-biopsy (4 males, 8 Del19 and 7 L858R EGFR mutations). 15/16 samples from re-biopsies and 9/16 samples from pre-osimertinib biopsies proceeded to OCA analyses. Others were excluded because of low quality of extracted nucleic acids. The acquired resistance mechanisms were as follows: T790M maintained in 10 patients with EGFR G796S being found in 1 patient. T790M loss observed in 5 patients with 1 patient having copy number gain in growth-arrest specific gene 6 (GAS6). Another patient possibly had copy number alterations in cell cycle genes. All patients had equal or reduced mutation counts during the therapeutic course, suggesting clonal selections by the therapies. Conclusions: EGFR C797S mutation was not observed in this series. Copy number alteration in GAS6-AXL pathway and cell cycle pathway could be targets of therapy. Citation Format: Atsushi Osoegawa, Masafumi Yamaguchi, Tomomi Nakamura, Ryotaro Morinaga, Kentaro Tanaka, Kosuke Kashiwabara, Kenichi Taguchi, Kazuki Nabeshima, Junji Kishimoto, Kenji Sugio. Revealing the mechanisms of acquired resistance to osimertinib from re-biopsy specimens in advanced non-small cell lung cancer with EGFR T790M mutation (LOGIK1607) [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr B004. doi:10.1158/1535-7163.TARG-19-B004