A Study of the Combination of Osimertinib, Platinum and Etoposide for Patients With Metastatic EGFR Mutant Lung Cancers

Inclusion Criteria: * Written informed consent * Advanced biopsy-proven metastatic non-small cell lung cancer * Either have not started an EGFR TKI or may have started osimertinib within the last 9 weeks * Somatic activating mutation in EGFR in pre-treatment tumor biopsy or cfDNA * Evidence of a concurrent P53 alteration by IHC or NGS on pre-treatment tumor biopsy or cfDNA * Evidence of a concurrent RB1 alteration by IHC or NGS on pre-treatment tumor biopsy or cfDNA * Must have a site of disease amenable to repeat biopsy and be willing to undergo a biopsy during treatment * Measurable (RECIST 1.1) indicator lesion not previously irradiated * Karnofsky performance status (KPS) ≥ 70% * Age \>18 years old * Ability to swallow oral medication * Adequate organ function * AST, ALT ≤ 3 x ULN * Total bilirubin ≤ 1.5x ULN * Creatinine ≤ 1.5x ULN OR calculated creatinine clearance ≥ 60ml/min * Absolute neutrophil count (ANC) ≥ 1000 cells/mm\^3 * Hemoglobin≥8.0 g/dL * Platelets ≥100,000/mm\^3 Exclusion Criteria: * Pregnant or lactating women * Started an EGFR TKI other than osimertinib or started osimertinib more than 9 weeks ago * Any radiotherapy within 1 week of starting treatment on protocol. * Any major surgery within 1 weeks of starting treatment on protocol. * Any evidence of active clinically significant interstitial lung disease * Continue to have unresolved \> grade 1 toxicity from any previous treatment * Have pure small cell histology * Corrected QT interval using Fridericia's formula (QTcF)\>475msec or any clinically significant (as deemed by the investigator) abnormalities in rhythm or conduction or morphology of the resting EKG. * Patients are to be excluded from cisplatin treatment arm if they meet any of the following criteria: * Creatinine clearance \< 60 ml/min * Hearing impairment requiring assistive device * Neuropathy * The treating provider does not feel as though the patient should receive cisplatin