RESUMO
BACKGROUND/AIM: Osimertinib is the first-line treatment for patients with advanced epidermal growth factor receptor (EGFR) mutation-positive non-small cell lung cancer (NSCLC). The present study aimed to determine the previously unclarified association of osimertinib plasma trough concentrations with efficacy, adverse events, and genetic polymorphisms in Japanese patients with NSCLC harboring EGFR mutations. PATIENTS AND METHODS: In this prospective study, blood samples of 25 patients who received osimertinib were collected to measure plasma osimertinib concentrations and to genotypically characterize ATP-binding cassette subfamily B member 1 and ATP-binding cassette subfamily G member 2 polymorphisms. Plasma osimertinib concentrations were analyzed using validated multiple reaction monitoring mode-based liquid chromatography-tandem mass spectrometry. Osimertinib concentration necessary to achieve optimal median progression-free survival (PFS) was determined using receiver operating characteristic curve analysis. PFS and overall survival were analyzed using the Kaplan-Meier method, and between-group differences were compared using the log-rank test. Plasma osimertinib concentrations between different patient groups were compared using the Mann-Whitney U-test. RESULTS: Patients were divided into high and low concentration groups based on a plasma osimertinib cut-off concentration of 211 ng/ml. Median PFS was longer in the high trough concentration group than that in the low trough concentration group (46.3 vs. 16.8 months, p=0.029). Plasma osimertinib concentrations adjusted for dose and body weight did not differ between the patients with and without variant polymorphisms. CONCLUSION: Monitoring plasma trough concentrations during maintenance might improve osimertinib treatment efficacy in patients with NSCLC harboring EGFR mutations.