Dynamic Changes of Circulating Tumor DNA in Late Stage NSCLC Patients

Inclusion Criteria: * Provision of informed consent * Histologically confirmed stage IIIB/IV NSCLC. * Activating EGFR mutations (G719A/C/S; Exon 19 insertion/deletion; L858R; L861Q) * Able to comply with the required protocol and followed-up procedures, and able to receive oral medications Exclusion Criteria: * Histologically confirmed small cell lung cancer or other metastatic tumors * Patient had received prior chemotherapy or EGFR-TKIs treatment * Patients who harbor Exon20 T790M mutation