P3.01-80 Retrospective Analysis of the Impact of EGFR T790M Mutation Detection by Re-Biopsy in Patients with NSCLC Harboring EGFR Mutations.

Abstract

EGFR-TKIs show a good response to most of patients with advanced non-small cell lung cancer (NSCLC) harboring EGFR activating mutations. However, it ultimately becomes the acquired resistance to EGFR-TKIs after various periods. We currently attempt to detect EGFR-T790M mutation by re-biopsy that induced a half of acquired resistances to them, because the third generation EGFR-TKI osimertinib had an effective response against the refractory tumors with EGFR-T790M mutations. However, the re-biopsy from tumors is relatively invasive and some cases are impossible to perform them. Therefore, it is a critical issue to select the population with EGFR-T790M mutations. In this study, we analyzed the refractory cases to initial EGFR-TKIs with successful re-biopsy samples to disclose these clinical questions. 78 advanced NSCLC patients with EGFR mutations who had successful re-biopsy samples after the resistance to initial EGFR-TKI treatment are enrolled at five institutions in Japan. We validated for the association between the emergence of EGFR-T790M mutation and their profiles, such as clinical outcomes with EGFR-TKI treatment and EGFR activating mutation status. s Of 78 advanced NSCLC patients with EGFR mutations, 39 cases were EGFR-T790M positive and 39 were negative in the re-biopsy samples. Of EGFR-T790M positive patients, 2 cases achieved a complete response (CR), 33 a partial response (PR), and 4 stable disease (SD). In contrast, 1 patient experienced a CR, 19 a PR, 18 SD, and 1 progressive disease (PD) in T790M negative patients. The objective response rate was higher in patients with T790M positive mutations than in those with T790M negative mutations (89.7% versus 51.2%, p< 0.01). There were no differences between each patients in progression free survival and time to failure treated with initial EGFR-TKIs. The response to initial EGFR TKI treatment might be one of good predictors for emerging of refractory tumors with EGFR-T790M mutations. Further experiments are needed to identify them.