P2.01-76 Bone Metastasis and Pleural Dissemination as a Potential Marker for Predicting of T790M Mutation in Advanced Non-Small Cell Lung Cancer Patients

Acquired resistance in epidermal growth factor receptor (EGFR)-mutated non-small-cell lung cancer (NSCLC)-patients after tyrosine kinase inhibitor (TKI)-treatment is a major clinical problem. In the majority of these patients, the T790M-mutation is detected at time of acquired TKI-resistance. However, it is less clear if the location of metastatic site may influence the ability to identify T790M mutation in NSCLC patients. We retrospectively screened patients with NSCLC harboring EGFR mutations with progressive disease who were rebiopsied between January 2016 and December 2018. EGFR T790M mutation status after EGFR-TKIs failure was assessed using liquid biopsy or tissue rebiopsy sample. Clinical factors influencing T790M status were evaluated by univariate and multivariate analysis. Among 39 rebiopsied patients for whom EGFR mutation status was available, 21 (53.8%) had T790M mutations. Patient characteristics at rebiopsy were not significantly different between T790M-positive and -negative groups, except for bone metastasis. Total duration of EGFR-TKI treatment before rebiopsy, EGFR-TKI treatment history immediately before rebiopsy, progression-free survival after initial TKI treatment, and rebiopsy site (other than fluid samples) significantly influenced T790M status. The incidence of T790M mutation was shown by multivariate analysis to be significantly higher in patients with bone metastasis and pleural dissemination (odds ratio, 26.4; 95% confidence interval (CI), 3.80-184 and odds ratio, 12.1; 95% CI, 1.57-92.4, respectively). Bone metastasis and pleural dissemination may represent useful predictive markers for T790M detection. In patients with these clinical factors, rebiopsies may be more recommended to detect T790M mutation.