Study of Durvalumab Following Radiation Therapy in Patients With Stage 3 Unresectable NSCLC Ineligible for Chemotherapy

Inclusion Criteria: 1. Capable of giving signed informed consent. 2. Age ≥ 18 years at study entry. 3. Histologically or cytologically documented NSCLC with locally-advanced, unresectable Stage III disease. 4. Deemed ineligible for chemotherapy per Investigator assessment. 5. Receipt of radiation therapy that was completed within 42 days prior to first study drug administration. 6. Must have received a total dose of radiation of 40 to 66 Gy (standard or hypofractionated BED). 7. Must not have progressed following radiation therapy, as per Investigator assessed RECIST 1.1 criteria: a) Patients with measurable disease and/or nonmeasurable and/or no evidence of disease assessed at baseline by computed tomography /magnetic resonance imaging will be eligible for this study. b) Prior irradiated lesions may be considered measurable and selected as target lesions (TLs) providing they fulfill the other criteria for measurability. 8. World Health Organization/ECOG performance status of ≤2. 9. No prior exposure to immune-mediated therapy including, but not limited to, anti-CTLA-4, anti-PD-1, anti-PD-L1, and antiprogrammed cell death ligand 2 (anti-PD-L2) antibodies, excluding therapeutic anticancer vaccines. 10. Patients must have adequate organ and marrow function as defined below: * Hemoglobin ≥ 9.0 g/dL * Absolute neutrophil count ≥ 1.0 × 109 /L * Platelet count ≥ 75 × 109/L * Serum bilirubin ≤ 1.5 × the upper limit of normal (ULN). This will not apply to patients with confirmed Gilbert's syndrome. * Alanine aminotransferase and aspartate aminotransferase ≤ 2.5 × ULN * Measured creatinine clearance \> 30 mL/min or calculated CL \> 30 mL/min as determined by Cockcroft-Gault 11. Life expectancy of greater than 12 weeks. 12. Body weight greater than 30 kg at study entry and at first study drug administration Exclusion Criteria: 1. Patients with locally-advanced NSCLC whose disease has progressed following radiation therapy. 2. Mixed small cell lung cancer and NSCLC histology. 3. History of allogeneic organ transplantation. 4. Active or prior documented inflammatory bowel disease (e.g., Crohn's disease, ulcerative, systemic lupus erythematosus, Sarcoidosis syndrome, or Wegener syndrome). 5. Uncontrolled intercurrent illness (e.g., ongoing or active infection, symptomatic congestive heart failure, uncontrolled hypertension, unstable angina pectoris) 6. History of another primary malignancy except for (a) malignancy treated with curative intent and with no known active disease ≥ 5 years before the first study drug administration, (b) adequately treated nonmelanoma skin cancer or lentigo maligna without evidence of disease, and c) treated carcinoma in situ without evidence of disease. 7. History of leptomeningeal carcinomatosis 8. History of active primary immunodeficiency 9. Active infection including tuberculosis, hepatitis B, hepatitis C, or human immunodeficiency virus 10. Any unresolved toxicity NCI CTCAE Grade ≥ 2 from previous anticancer therapy with the exception of alopecia, vitiligo, lymphopenia, and the laboratory values defined in the inclusion criteria 11. Known allergy or hypersensitivity to any of the study drugs or any of the study drug excipients. 12. Receipt of live attenuated vaccine within 30 days prior to the first dose of durvalumab 13. Major surgical procedure (as defined by the Investigator) within 28 days prior to the first dose of durvalumab. 14. Current or prior use of immunosuppressive medication within 14 days before the first dose of durvalumab. 15. Participation in another clinical study with an IP administered in the last 4 weeks. 16. Concurrent enrollment in another clinical study, unless it is an observational (noninterventional) clinical study or during the follow-up period of an interventional study 17. Prior randomization or treatment in a previous durvalumab clinical study regardless of treatment arm assignment 18. Patients who refuse chemotherapy by their own decision. 19. Involvement in the planning and/or conduct of the study 20. Female patients who are pregnant or breastfeeding or male or female patients of reproductive potential who are not willing to employ effective birth control. 21. Judgment by the Investigator that the patient should not participate in the study 22. Genetics research study (optional): Exclusion criteria for participation in the optional genetics research component of the study include: a) Previous allogeneic bone marrow transplant b)Nonleukocyte-depleted whole blood transfusion within 120 days of genetic sample collection.