The study will investigate whether PD-L1 and other immuno-markers will be influenced by
osimertinib treatment in advanced epidermal growth factor receptor （EGFR）T790M positive
advanced NSCLC patients. In addition, we will explore whether PD-L1 and other immuno-markers
can predict the safety and efficacy of subsequent use of immune checkpoint inhibitors at the
time of PD due to osimertinib resistance.