Durvalumab With Stereotactic Body Radiation Therapy (SBRT) vs Placebo With SBRT in Early Stage Unresected Non-small Cell Lung Cancer (NSCLC) Patients/ Osimertinib Following SBRT in Patients With Early Stage Unresected NSCLC Harboring an EGFR Mutation

Main Cohort Key 1. Age ≥18 years 2. Planned SoC SBRT as definitive treatment 3. World Health Organization (WHO)/ECOG PS of 0, 1 or 2 4. Life expectancy of at least 12 weeks 5. Body weight \>30 kg 6. Submission of tumor tissue sample if available 7. Adequate organ and marrow function required 8. Patients with central or peripheral lesions are eligible 9. Staging studies must be done during screening (PET-CT within 10 weeks) 10. Patients with a history of metachronous NSCLC and synchronous lesions are eligible with some exceptions Main Cohort Key

1. Mixed small cell and non-small cell cancer 2. History of allogeneic organ transplantation 3. History of another primary malignancy with exceptions 4. History of active primary immunodeficiency 5. Epidermal growth factor receptor local testing is strongly recommended prior to enrollment. Patients with a tumor harboring an EGFRm per local testing will be excluded from the main cohort 6. Prior exposure to immune-mediated therapy with exceptions Osimertinib Cohort Key Inclusion Criteria 1. Age ≥18 years 2. Planned SoC SBRT as definitive treatment 3. WHO/ECOG PS of 0, 1, or 2 4. Patients with central or peripheral lesions are eligible 5. Patients with a history of metachronous NSCLC and synchronous lesions are eligible with some exceptions 6. Staging studies must be done during screening (PET-CT within 10 weeks) 7. Submission of tumor tissue sample if available 8. Confirmation by local laboratory that the tumor harbors one of the 2 common EGFR mutations known to be associated with EGFR-TKI sensitivity (Ex19del, L858R) 9. Adequate bone marrow reserve or organ function required 10. Female patients should be using highly effective contraceptive measures 11. Male patients should be asked to use barrier contraceptives (ie, condoms) during sex with all partners during the trial and avoid procreation Osimertinib Cohort Key