Osimertinib Alone or With Chemotherapy for EGFR-Mutant Lung Cancers

Screening portion: Patients will begin on single agent osimertinib obtained commercially at the standard dose of 80mg orally daily. Osimertinib monotherapy is currently standard of care first-line treatment for patients with metastatic EGFR-mutant lung cancers. During the screening portion of the study, patients will be treated per standard practice as decided by the treating physician using the guidance of the osimertinib product label. The patient will proceed with three cycles (21 days per cycle) of single agent osimertinib. Patients will be seen on C1D1 for osimertinib start (telemedicine visits for C1D1 assessments are acceptable) Randomization/treatment portion: Patients will be randomized to continue osimertinib alone (Arm A) or addition of carboplatin/pemetrexed chemotherapy to osimertinib (Arm B).Randomization will be accomplished by the method of random permuted block and patients will be stratified by type of EGFR mutation (EGFR exon 19/EGFR L858R or other) and presence of CNS metastases (absent, present). Randomization will occur after data is available to identify the patients with persistent EGFR ctDNA detected in the C2D1 plasma sample; only patients with persistent EGFR ctDNA will be randomized. Subject's eligibility prior to randomization will be at the discretion of the individual sites enrolling the patients. EGFR mutation can be confirmed at outside institutions: while pathology confirmation will occur at the enrolling institution, the required documentation of EGFR can occur internal or external to the enrolling institution. For those patients without detectable ctDNA at C2D1, the end of treatment assessments will not include CT scan or ctDNA sampling.