A Study to Evaluate Chemotherapy Plus Osimertinib Against Chemotherapy Plus Placebo in Patients With Non-small Cell Lung Cancer (NSCLC)

Inclusion Criteria: 1. Capable of giving signed informed consent, which includes compliance with the requirements and restrictions listed in the informed consent form and in this protocol. 2. Pathologically confirmed non-squamous NSCLC. 3. Locally advanced (clinical stage IIIB or IIIC) or metastatic NSCLC (clinical stage IVA or IVB) or recurrent NSCLC, not amenable to curative surgery or radiotherapy. 4. Evidence of radiological extracranial disease progression following (Investigator-assessed) response or SD for ≥ 6 months during first-line osimertinib treatment, but who have not received further, subsequent treatment. 5. Tumor known to harbor 1 of the 2 or both common epidermal growth factor receptor (EGFR) mutations known to be associated with EGFR tyrosine kinase inhibitor (TKI) sensitivity (Ex19del or L858R), either alone or in combination with other EGFR mutations, which may include T790M. 6. World Health Organization performance status of 0 to 1 at screening with no clinically significant deterioration in the previous 2 weeks. 7. Life expectancy \>12 weeks at Day 1. 8. At least 1 lesion, not previously irradiated, that can be accurately measured. 9. Females must be using highly effective contraceptive measures, and must have a negative pregnancy test prior to start of dosing if of childbearing potential, or must have evidence of non-childbearing potential by fulfilling criteria at screening. 10. Male patients must be willing to use barrier contraception Exclusion Criteria: 1. Clinical or radiological evidence of CNS progression on first-line osimertinib. 2. Past medical history of interstitial lung disease (ILD)/pneumonitis, drug-induced ILD/pneumonitis, radiation pneumonitis that required steroid treatment, or any evidence of clinically active ILD/pneumonitis. 3. Any evidence of severe or uncontrolled systemic diseases. 4. Any of the following cardiac criteria: i) Mean resting QTc \>470 msec ii) Any clinically important abnormalities in rhythm, conduction, or morphology of resting electrocardiogram iii) Any factors that increase the risk of QTc prolongation or risk of arrhythmic events 5. Any concurrent and/or other active malignancy that has required treatment within 2 years of first dose of investigational product (IP). 6. Any unresolved toxicities from prior therapy. 7. Refractory nausea and vomiting, chronic gastrointestinal diseases, inability to swallow the formulated product, or previous significant bowel resection that would preclude adequate absorption of osimertinib. 8. More than 4 weeks elapsed since last dose of osimertinib by date of randomization. 9. Unable to tolerate osimertinib 80 mg first-line therapy. 10. Prior treatment with any systemic anti-cancer therapy. 11. Major surgery within 4 weeks of the first dose of IP. 12. Radiotherapy treatment to more than 30% of the bone marrow or with a wide field of radiation within 4 weeks of the first dose of IP. 13. Current use of medications or herbal supplements known to be strong inducers of cytochrome P450 (CYP) 3A4. 14. Participation in another clinical study with an IP other than first-line osimertinib during the 4 weeks prior to Day 1.