- Prior neoadjuvant or adjuvant chemotherapy treatment within 6 months prior to starting 1st EGFR TKI treatment - Treatment with more than one prior line of treatment for advanced NSCLC - Treatment with an approved EGFR-TKI (e.g. erlotinib, gefitinib, afatinib) within 8 days or approximately 5x half-life of the first dose of study treatment - Any investigational agents or other anticancer drugs from a previous treatment regimen or clinical study within 14 days of the first dose of study treatment - Previous treatment with Osimertinib, or a 3rd generation EGFR TKI For subjects who cross over to Osimertinib: - Once subjects on the platinum-based doublet chemotherapy arm are determined to have objective radiological progression according to RECIST 1.1 by the investigator and confirmed by an independent central imaging review. - At least 14 days since the last dose of platinum-based doublet chemotherapy.