Quick Start Durvalumab Following Chemoradiation for Stage III Nonsmall Cell Lung Cancer

Inclusion Criteria: * Patients must have stage II or stage III NSCLC confirmed by histologic or cytologic documentation and by clinical assessment. Staging is defined according to the AJCC Cancer Staging Manual, 8th Edition (2017). * Unresectable or medically inoperable as determined by the investigator. * The patient has definitive radiation therapy (e.g., 54 Gy to 66 Gy in 30 to 35 fractions) for lung cancer that is either (a) planned to start within the next 28 days, or (b) currently being administered, or (c) has been completed within the last 14 days. * Platinum-based chemotherapy for lung cancer that is either (a) planned to start within the next 28 days, (b) currently being administered, or (c) has been completed within the last 14 days. Chemotherapy must be for at least two cycles and be administered either before radiation therapy ("induction" or "sequential") or during radiation therapy ("concurrent"). * Consolidation durvalumab is planned for NSCLC after radiation and chemotherapy. * Eighteen years old or greater. * ECOG performance status of 0-2. * Life expectancy of greater than three months. * Patients with sexual relationships in which either they or their partner may become pregnant must use contraception during the study treatment period. * Ability to understand and be willing to sign an IRB-approved informed consent document directly or via a legally authorized representative. Exclusion Criteria * Uncontrolled respiratory symptoms (i.e., cough, dyspnea, fevers, chest pain, or an increase from baseline oxygen requirements) that are interfering with activities of daily living. * Nonsmall cell lung cancer is known to have a tumor with a mutation in EGFR associated with sensitivity to first-line therapy with a tyrosine kinase inhibitor (i.e., Ex19del or L858R). Testing for EGFR mutation must have been attempted for study enrollment. If EGFR testing is inconclusive (e.g., the biopsy's quantity or quality is not sufficient for testing to be performed) and there is low clinical suspicion for the presence of an EGFR mutation as determined by the investigator, then the patient is eligible. * Prior exposure to an immune checkpoint inhibitor targeting CTLA-4, PD-1, or PD-L1. * Active autoimmune disease requiring systemic immunosuppression at the time of enrollment. * History of autoimmune pneumonitis requiring high-dose systemic steroids (equivalent prednisone \>20 mg/day for more than one week). * Uncontrolled intercurrent illness includes ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements. * Patients who are pregnant or breastfeeding.