Osimertinib and Gefitinib in EGFR Inhibitor naïve Advanced EGFR Mutant Lung Cancer

Inclusion Criteria: * Participants must have histologically confirmed stage IV NSCLC (per AJCC 7th edition) with either the L858R or exon 19 deletion activating EGFR mutation as identified in a CLIA-approved laboratory. Note: recurrent stage IV disease initially diagnosed at an earlier stage is considered eligible, provided prior treatment criteria is met. * Participants must have measurable disease, defined as at least one lesion that can be accurately measured in at least one dimension (longest diameter to be recorded for non-nodal lesions and short axis for nodal lesions) as ≥20 mm with conventional techniques or as ≥10 mm with spiral CT scan, MRI, or calipers by clinical exam. * Participants can have no prior history of any EGFR-directed therapy, including TKIs or antibodies, and must also be chemotherapy and immunotherapy naïve. Patients who have completed adjuvant or neo-adjuvant chemotherapy or immunotherapy \>6 months ago are considered treatment naive. * Participants must be aged ≥ 18 years * Participants must have an ECOG performance status of 0-1 (Appendix A) * Participants must have a life expectancy of greater than 12 weeks * Participants must have normal organ and marrow function as defined below: * leukocytes ≥3,000/mcL * absolute neutrophil count ≥1,500/mcL * platelets ≥100,000/mcL * hemoglobin \>9.0 g/dL * total bilirubin \< 1.5 times the ULN if no liver metastases or \< 3 times the ULN in the presence of documented Gilbert's syndrome (unconjugate…