This study will assess the efficacy and safety of single-agent osimertinib in patients with locally advanced or metastatic EGFR T790M-positive NSCLC within the context of the early access program in Hong Kong. In particular, osimertinib treatment efficacy will be assessed in the context of the relationship between EGFR T790M mutant AF and survival outcomes, particularly overall survival. In a real-world setting, analysis of overall survival benefit is considered less sensitive to differences in healthcare systems and standards. Other clinical outcomes including response rate (based on physician's judgement) and time to treatment discontinuation (TTD) will be examined. This study will also describe current practice for molecular testing and EGFR mutation profiles in this patient population.