Background: Systemic chemotherapy for first-line (1L) metastatic NSCLC shows mixed outcomes. Results from studies using immunotherapy alone or combined with chemotherapy as 1L treatment in patients (pts) with metastatic NSCLC represent a substantial advance, but further improvement is needed. Increased DNA damage triggered by polyadenosine 5’diphosphoribose polymerase inhibition may confer antitumor activity, modify tumor immunogenicity, and further sensitize tumors to immune checkpoint inhibition, thus promoting a more durable antitumor response. This Phase 2, randomized, multicenter, double-blind study (NCT03775486) is designed to assess the efficacy and safety of durvalumab + olaparib vs durvalumab alone as maintenance therapy in pts whose Stage IV NSCLC has not progressed following 1L platinum-based chemotherapy + durvalumab. Methods: Adult pts with Stage IV NSCLC with tumors lacking activating EGFR mutations and ALK fusions are eligible. In the initial therapy phase, all pts will receive durvalumab (1500 mg IV) concurrent with platinum-based doublet therapy. Durvalumab + chemotherapy will be administered for 4 cycles for both squamous NSCLC (nanoparticle albumin-bound [nab]-paclitaxel + carboplatin or gemcitabine + carboplatin/cisplatin) and nonsquamous NSCLC (nab-paclitaxel + carboplatin or pemetrexed + carboplatin/cisplatin). Pts whose disease does not progress (complete or partial response [CR/PR] or stable disease [SD]; investigator-assessed RECIST 1.1) will be randomized (1:1) to durvalumab (1500 mg IV, every 4 weeks) + either olaparib (300 mg, oral, BID) or its matching placebo until disease progression. Randomization will be stratified based on objective response to durvalumab + chemotherapy (CR/PR or SD) during the initial therapy phase and histology (squamous or nonsquamous). The primary endpoint is PFS (investigator-assessed, RECIST 1.1). Secondary endpoints are OS, PFS in pts with homologous recombination repair related gene mutation, ORR, duration of response, HRQoL, pharmacokinetics and immunogenicity of durvalumab, and safety. Pt enrollment is ongoing. Clinical trial information: NCT03775486