EGFR tyrosine kinase inhibitor (TKI) can significantly improve objective response rate (ORR) and prolong progression free survival (PFS) in EGFR mutated locally advanced or metastatic NSCLC patients compared to platinum-based chemotherapy, with less adverse events and higher quality of life (QoL).Osimertinib is an oral, potent, irreversible third-generation EGFR TKI that is selective for EGFR TKI sensitizing mutation and the T790M resistance mutation. Two phase 2 studies(AURA extension, AURA2)have demonstrated encouraging efficacy and tolerable toxicity.However, local data reflecting testing status including testing platform, sample tested, and turnaround time in China is still lacking. The current study will not only assess the effectiveness of osimertinib treatment in a real world setting, but will also help us to understand the real-world testing patterns among T790M mutation positive locally advanced or metastatic NSCLC patients who have progressed after EGFR TKI treatment.Objectives and Hypotheses:The objective of this study is to assess osimertinib effectiveness among locally advanced or metastatic T790M mutation positive NSCLC patients who have progressed after EGFR TKI therapy.The specific study objectives that will be assessed include the following:Primary Objective§ To assess the real world effectiveness of osimertinib treatment in locally advanced or metastatic NSCLC patients with a EGFR T790M mutation in terms of response rate (RR)Secondary Objectives§ To assess the real world effectiveness of osimertinib treatment in locally advanced or metastatic NSCLC patients with a EGFR T790M mutation in terms of progression free survival (PFS)§ To describe the pattern of T790M mutation testing, including turnaround time, sample type, testing techniques, EGFR subtype, T790M mutation abundance if tested quantitatively.§ To assess the real world safety profile of osimertinib§ To describe the treatment pattern including treatment lines and combination therapy (radiotherapy, surgery, etc.) in a real world setting