Abstract CT106: Phase I/II study of osimertinib in EGFR exon 20 insertion mutations in non-small cell lung cancer patients: AEX20
Authors: Ichihara Eiki , Yasuda Hiroyuki , Takashima Yuta , Zenke Yoshitaka , Takeuchi Shinji , Morise Masahiro , Hotta Katsuyuki , Sato Mineyoshi , Matsumoto Shingo , Tanimoto Azusa , Matsuzawa Reiko , Kiura Katsuyuki , Terai Hideki , Ikemura Shinnosuke , Goto Koichi , Soejima Kenzo 
Published: July 2021

Background EGFR exon 20 insertion gene mutation (ex20ins) accounts for about 4-12% of the total EGFR gene mutations in non-small cell lung cancer (NSCLC) patients. NSCLC patients with EGFR ex20ins is known to be less sensitive to 1st- or 2nd-generation EGFR-TKIs. Although 3rd-generation EGFR-TKI, osimertinib is active against in vitro models of EGFR ex20ins, its efficacy has not yet been fully elucidated. This phase I/II study is conducted to evaluate the clinical efficacy of osimertinib in NSCLC patients with EGFR ex20ins. Method This is a single-arm, multi-center, open-label, non-randomized phase I/II study (UMIN000031929) consisting of stage 1 and stage 2 (Simon's two-stage design). In stage 1, 12 patients receive osimertinib 80mg once daily until they meet the termination criteria, such as, disease progression, severe toxicities, withdrawal etc. In stage 2, 9 patients receive the same dose of osimertinib if more than 1 patient achieve PR or CR in stage 1. At the transition from stage 1 to 2, Independent Data Monitoring Committee (IDMC) will provide recommendation regarding the need for study continuation, termination or dose modification of osimertinib. Patients with advanced or metastatic NSCLC with EGFR ex20ins who have a history of chemotherapy within 0 to 3 regimens are enrolled. Patients with history of EGFR-TKI treatment (gefitinib, erlotinib, afatinib, dacomitinib) can be included if the EGFR-TKI treatment did not show any clinical benefit. Patients with EGFR gene mutations, such as exon 19 deletion, L858R, T790M, G719X, L861Q are excluded. Primary end point is objective response rate (ORR) assessed via Response Evaluation Criteria in Solid Tumors version 1.1. Secondary end points are progression-free survival, overall survival, and safety profiles. Blood sampling is obtained at 4-weeks after starting osimertinib to analyze pharmacokinetic parameters. We also perform liquid biopsy for next generation sequencing at before and after acquiring resistance to osimertinib to clarify resistant mechanisms of osimertinib in EGFR ex20ins. We explore the relationship among clinical outcome, side effect, pharmacokinetic parameters and subtype of EGFR ex20ins. Result Recruitment began in June 2018 and by February 2020, 12 patients were enrolled in stage 1 at 6 institutions. Backgrounds of the patients were as follows, the median age was 63 years (range 22-84), female/male 6/6, ECOG PS 0/1 8/4, cStage IIIA/IIIb/IVA/IVB 1/1/2/8. The ORR was 0% (CR/PR 0, SD 8, PD 4), and the DCR was 66.7%. From the result of stage 1, one of the IDMC's recommendations was protocol revision since it is presumed that increasing the dose of osimertinib could be clinically promising. At the conference, the influence of subtype of EGFR ex20ins and blood levels of osimertinib on survival will be evaluated and the results of interim analysis for stage 1 will be presented. Conclusion Regular dose of osimertinib has limited clinical activity in NSCLC patients with EGFR ex20ins. Funding AstraZeneca.

Citation Format: Eiki Ichihara, Hiroyuki Yasuda, Yuta Takashima, Yoshitaka Zenke, Shinji Takeuchi, Masahiro Morise, Katsuyuki Hotta, Mineyoshi Sato, Shingo Matsumoto, Azusa Tanimoto, Reiko Matsuzawa, Katsuyuki Kiura, Hideki Terai, Shinnosuke Ikemura, Koichi Goto, Kenzo Soejima. Phase I/II study of osimertinib in EGFR exon 20 insertion mutations in non-small cell lung cancer patients: AEX20 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT106.