496P - Higher osimertinib introduction rate achieved by multiple repeated re-biopsy after acquired resistance to first/second generation EGFR-TKIs

Abstract

BackgroundIndication for treatment with osimertinib after first/second generation epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) resistance depends on T790M mutation detected by re-biopsy. REMEDY trial consisting many cases using plasma biopsy revealed osimertinib introduction rate of approximately 25 percent in EGFR-mutant non-small cell lung cancer (NSCLC) patients pretreated with first/second generation EGFR-TKIs. The aim of study is to analyze the data on clinical practice of our hospital, where histological re-biopsy is actively carried out multiple times. MethodsWe retrospectively reviewed our electronic medical records of EGFR-mutant NSCLC patients to examine osimertinib introduction rate and associated outcomes. ResultsAmong 95 patients with EGFR-mutant NSCLC, 73 patients received first/second generation EGFR-TKIs. Of 57 progressive disease patients, 50 patients (57/50: 87%) underwent re-biopsy. T790M was detected in 36 patients (36/50: 72%) and osimertinib was introduced in 35 patients (35/50: 70%). Among 36 patients harboring T790M mutation: histological re-biopsy was performed in 21 patients (21/36: 58%); cytology in 12 patients (12/36: 33%); blood biopsy in three patients (3/36: 8.3%). T790M was detected by first re-biopsy in 14 patients (14/36: 39%), and by second or subsequent re-biopsy 22 patients (22/36: 61%). The median overall survival (OS) in osimertinib induction patients was not reached (95% CI, 64.2-not reached) while in non- osimertinib patients median OS was 92.9 months (95% CI, 22.5-not reached) (p = 0.0173). Five year survival rates were 77% and 52%, respectively. ConclusionsHigher osimertinib introduction rate was achieved by multiple repeated re-biopsy after first/second generation EGFR-TKIs, and its high introduction rate could contribute to better prognosis of EGFR-mutant NSCLC. Legal entity responsible for the studyKobe Minimally Invasive Cancer Center. FundingHas not received any funding. DisclosureAll authors have declared no conflicts of interest.