Abstract 4920: A status of re-biopsy for non-small-cell lung cancer patients after first EGFR-TKI failure and incidence of T790M mutation
Authors: Sakai Tetsuya , Udagawa Hibiki , Zenke Yoshitaka , Kirita Keisuke , Umemura Shigeki , Matsumoto Shingo , Yoh Kiyotaka , Niho Seiji , Ishii Genichiro , Goto Koichi 
Published: August 2019

Abstract
Background: Among patients with advanced non-small-cell lung cancer (NSCLC) harboring epidermal growth factor receptor (EGFR) mutation, T790M mutation is the most common mechanism of drug resistance to first- or second-generation EGFR tyrosine kinase inhibitors (TKIs). However, the proportion of patients with T790M mutation at re-biopsy is varied by studies or biopsy methods.
Methods: A total of 126 patients who were treated with first- or second-generation EGFR TKIs and had disease progression in our institution from January 2017 to September 2018 were eligible for this study. We retrospectively evaluated re-biopsy methods and the proportion of patients who harbor T790M mutation.
Result: A total of 126 patients (male, 36.5% ; median age, 69 year ) were included. Among 126 patients, 118 patients (93.7%) underwent re-biopsy by any methods: tissue biopsy or cytology sampling in 68 patients and plasma sampling in 50 patients during a first re-biopsy, and 44 patients (37.3%) had T790M mutation. During the first biopsy, in the 68 patients who underwent tissue biopsy or cytology sampling, 32 patients (47%) were positive for T790M mutation, nevertheless there were no tumor samples in 4 patients and only atypical cells in 3 patients and 1 patient was identified transformation to SCLC. In the 50 patients who performed plasma sampling during a first re-biopsy, T790M mutation was detected in only 12 patients (24%). Second re-biopsy was conducted in 19 patients among 74 patients resulted in T790M-negative or unknown after the first re-biopsy, and 10 patients were positive for T790M mutation. Eventually, a total of 80 patients were performed tissue biopsy or cytology sampling, 74 patients (96.1%) were found to have any EGFR mutations and T790M mutation was detected in 39 patients (48.1%). On the other hand, 59 patients underwent plasma sampling and 31 patients (52.5%) were found to have any EGFR mutations and T790M mutation was detected in only 17 patients (28.8%). Totally 54 patients (42.9%) were detected T790M mutation, and 52 patients (41.3%) received Osimertinib subsequently.
Conclusion: After progression of first- or second-generation EGFR-TKIs, about 95% of patients underwent re-biopsy, and T790M mutation was present in approximately half of patients who underwent re-biopsy and almost all patients who were positive for T790M mutation could receive Osimertinib. In patients who underwent tissue biopsy or cytology sampling, high frequency of detecting any EGFR mutations contributed to higher detection rate of T790M mutation compared to plasma sampling. To improve the sensitivity for T790M mutation detection, tissue biopsy or cytology sampling should be performed if possible.
Citation Format: Tetsuya Sakai, Hibiki Udagawa, Yoshitaka Zenke, Keisuke Kirita, Shigeki Umemura, Shingo Matsumoto, Kiyotaka Yoh, Seiji Niho, Genichiro Ishii, Koichi Goto. A status of re-biopsy for non-small-cell lung cancer patients after first EGFR-TKI failure and incidence of T790M mutation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4920.