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

This is a Phase III, randomized, double-blind, placebo-controlled study of platinum plus pemetrexed chemotherapy plus osimertinib versus platinum plus pemetrexed chemotherapy plus placebo in patients with epidermal growth factor receptor mutation-positive (EGFRm), locally advanced or metastatic NSCLC with or wihout stable brain metastases who responded to first-line osimertinib therapy (complete response \[CR\] or partial response \[PR\]) or stable disease (SD) for ≥ 6 months during first-line osimertinib treatment, and subsequently experienced radiological, extracranial disease progression. Approximately 204 patients were to be randomized in a 1:1 ratio to treatment with platinum plus pemetrexed chemotherapy plus osimertinib (Treatment Arm A) or platinum plus pemetrexed chemotherapy plus placebo (Treatment Arm B). However, the number of patients has been reduced to approximately 80 patients due to treatment landscape changes which outpaced study recruitment. Patients will be stratified based on the presence of brain metastases (stable brain metastases based on central nervous system (CNS) Response Evaluation Criteria in Solid Tumors, Version 1.1 \[RECIST 1.1\] assessments versus no brain metastases). The 2 randomized treatment regimens are as follows: * Treatment Arm A: Osimertinib 80 mg once daily (QD) with pemetrexed (500 mg/m\^2) (with pre-treatment) plus either cisplatin (75 mg/m\^2) or carboplatin (area under the concentration-time curve \[AUC\] 5), both administered on Day 1 of 21-day cycles for 4 cycles, followed by osimertinib 80 mg QD plus pemetrexed maintenance (500 mg/m\^2) on Day 1 of 21-day cycles * Treatment Arm B: Placebo QD with pemetrexed (500 mg/m\^2) (with pre-treatment) plus either cisplatin (75 mg/m\^2) or carboplatin (AUC5), both administered on Day 1 of 21-day cycles for 4 cycles, followed by placebo QD plus pemetrexed maintenance (500 mg/m\^2) on Day 1 of 21-day cycles.