Osimertinib Alone or With Chemotherapy for EGFR-Mutant Lung Cancers

Inclusion Criteria: Inital * Age ≥ 18 years * Biopsy proven metastatic non-small cell lung cancer, confirmed at enrolling institution * Somatic activating mutation in EGFR in pre-treatment tumor biopsy/ cytology from pleural fluid or cfDNA * Either have not started a prior EGFR TKI therapy or may have started osimertinib within 3 weeks of confirming eligibility and enrollment criteria of measurable disease per approval of PI, with no prior chemotherapy for treatment of metastatic disease (adjuvant therapy \> 6 months prior to study start is acceptable) * Measurable (RECIST 1.1) indicator lesion not previously irradiated with measurable disease determined per treating investigator. If a patient has already started on osimertinib there must be available pre-osimertinib baseline tumor assessments , or tumor assessments within +7 days of Osimertinib start, to be utilized for RECIST 1.1 assessment. * Karnofsky performance status (KPS)≥70%, * Ability to swallow oral medications * Adequate organ function (use of G-CSF and/or transfusion to meet these criteria are not allowed) * Hemoglobin ≥ 9 g/dL * Platelets ≥ 150,000mm\^3 or 150 x 10\^9/L * AST, ALT ≤ 2.5 x ULN with no liver metastases or \< 5x ULN with the presence of liver metastases * Total bilirubin ≤ 1.5 x ULN if no liver metastases or \< 3 x ULN in the presence of documented Gilbert's Syndrome (unconjugated hyperbilirubinemia) or liver metastases * Absolute neutrophil count (ANC) ≥ 1500 cells/mm\^3 * Creatinine…