Usefulness of Bronchoscopic Rebiopsy of Non-Small Cell Lung Cancer with Acquired Resistance to Epidermal Growth Factor Receptor-Tyrosine Kinase Inhibitor

: Background: Approximately 50% of non-small cell lung cancer (NSCLC) patients with acquired resistance to EGFR-TKI harbor the EGFR mutation T790M. The recent development and wide use of third-generation EGFR-TKIs targeting T790M-mutant NSCLCs have increased the importance of rebiopsy after EGFR-TKI failure. We aimed to investigate the advantages of flexible bronchoscopy as a rebiopsy method and the prevalence of and factors affecting the T790M mutation after EGFR-TKI failure. Methods: We investigated 139 patients who had undergone bronchoscopic rebiopsy and endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) between Sep 2014 and Jul 2016. Results: Among the 139 patients, bronchoscopic rebiopsy yielded successful pathological diagnoses in 102 (73.4%). Among them, 41 patients with EGFR-mutant lung adenocarcinoma and EGFR-TKI progression were selected for an investigation of T790M mutation prevalence at rebiopsy. The initial EGFR mutations were exon 19 del (56.1%), L858R or L861Q (34.1%), and others (9.8%). The most common rebiopsy method was transbronchial lung biopsy (41.5%), followed by EBUS-TBNA (26.8%) and endobronchial biopsy (19.5%). The median interval to T790M emergence was the longest among cases with exon 19 deletion (14.1 months), followed by exon 21 L858R or L861Q (11.3 months) and other rare EGFR mutations (2.9 months). The T790M mutation was identified in 18 (43.9%) patients, and exon 19 del was the most significant factor affecting T790M mutation development (hazard ratio: 6.875, P = 0.014). Conclusions: Bronchoscopy was more useful than other rebiopsy approaches. The T790M emergence rate was highest in cases with exon 19 deletion, likely as a consequence of long-term EGFR-TKI exposure.