Study of Durvalumab+Olaparib or Durvalumab After Treatment With Durvalumab and Chemotherapy in Patients With Lung Cancer (ORION)

Inclusion Criteria: \- Histologically or cytologically documented Stage IV NSCLC not amenable to curative surgery or radiation. Patients must have tumors that lack activating EGFR mutations and ALK fusions. * (WHO)/(ECOG) performance status of 0 or 1 * No prior chemotherapy or any other systemic therapy for Stage IV NSCLC * Adequate organ and marrow function without blood transfusions in the past 28 days, * At least 1 tumor lesion, not previously irradiated, that can be accurately measured as per RECIST 1.1. Key Inclusion criteria for randomization to maintenance treatment: * Documented radiographic evidence of CR, PR, or Stable Disease (SD) as per Investigator-assessed RECIST 1.1 following 4 cycles of platinum-based chemotherapy. * Creatinine Clearance (CrCl) ≥51 mL/min calculated by the investigator or designee using the Cockcroft-Gault equation or measured by 24-hour urine collection. * Ability to swallow whole oral medications. * All patients must provide a formalin-fixed, paraffin embedded tumor sample for tissue-based immunohistochemistry staining and DNA sequencing to determine PD-L1 expression, HRRm status, and other correlatives: either newly acquired or archival tumor samples (\<3 years old) are acceptable. If available, a newly acquired tumor biopsy, collected as part of routine clinical practice, is preferred. If not available, an archival sample taken \<3 years prior to screening is acceptable. If both an archival sample and a fresh tumor biopsy sample are available, both samples should be submitted for analysis and must be submitted as different samples using different accession numbers. Slides from different blocks cannot be mixed and submitted with the same kit. Exclusion criteria * Mixed small-cell lung cancer and sarcomatoid variant NSCLC histology. * Prior exposure to any chemotherapy agents (except chemotherapy or chemoradiation for non-metastatic disease), polyadenosine 5'diphosphoribose \[poly (ADP ribose)\] polymerase (PARP) therapy, or immunomediated therapy * Active or prior documented autoimmune or inflammatory disorders. * Any concurrent chemotherapy, IP, biologic, or hormonal therapy for cancer treatment. * Current or prior use of immunosuppressive medication within 14 days before the first dose of Investigational Product (IP) * untreated (CNS) metastases and/or carcinomatous meningitis * Active infection. Exclusion criteria to be randomized to maintenance treatment: • Inability to complete 4 cycles of platinum-based chemotherapy for any reason or discontinuation of Durvalumab during initial therapy.