Background: Patients with non-small-cell lung cancer (NSCLC) that is resistant to PD-1 and PD-L1 (PD[L]-1)-targeted therapy have poor outcomes. Studies suggest that radiotherapy could enhance antitumour immunity. Therefore, we investigated the potential benefit of PD-L1 (durvalumab) and CTLA-4 (tremelimumab) inhibition alone or combined with radiotherapy., Methods: This open-label, multicentre, randomised, phase 2 trial was done by the National Cancer Institute Experimental Therapeutics Clinical Trials Network at 18 US sites. Patients aged 18 years or older with metastatic NSCLC, an Eastern Cooperative Oncology Group performance status of 0 or 1, and progression during previous PD(L)-1 therapy were eligible. They were randomly assigned (1:1:1) in a web-based system by the study statistician using a permuted block scheme (block sizes of three or six) without stratification to receive either durvalumab (1500 mg intravenously every 4 weeks for a maximum of 13 cycles) plus tremelimumab (75 mg intravenously every 4 weeks for a maximum of four cycles) alone or with low-dose (0·5 Gy delivered twice per day, repeated for 2 days during each of the first four cycles of therapy) or hypofractionated radiotherapy (24 Gy total delivered over three 8-Gy fractions during the first cycle only), 1 week after initial durvalumab-tremelimumab administration. Study treatment was continued until 1 year or until progression. The primary endpoint was overall response rate (best locally assessed confirmed response of a partial or complete response) and, along with safety, was analysed in patients who received at least one dose of study therapy. The trial is registered with ClinicalTrials.gov, NCT02888743, and is now complete., Findings: Between Aug 24, 2017, and March 29, 2019, 90 patients were enrolled and randomly assigned, of whom 78 (26 per group) were treated. This trial was stopped due to futility assessed in an interim analysis. At a median follow-up of 12·4 months (IQR 7·8-15·1), there were no differences in overall response rates between the durvalumab-tremelimumab alone group (three [11·5%, 90% CI 1·2-21·8] of 26 patients) and the low-dose radiotherapy group (two [7·7%, 0·0-16·3] of 26 patients; p=0·64) or the hypofractionated radiotherapy group (three [11·5%, 1·2-21·8] of 26 patients; p=0·99). The most common grade 3-4 adverse events were dyspnoea (two [8%] in the durvalumab-tremelimumab alone group; three [12%] in the low-dose radiotherapy group; and three [12%] in the hypofractionated radiotherapy group) and hyponatraemia (one [4%] in the durvalumab-tremelimumab alone group vs two [8%] in the low-dose radiotherapy group vs three [12%] in the hypofractionated radiotherapy group). Treatment-related serious adverse events occurred in one (4%) patient in the durvalumab-tremelimumab alone group (maculopapular rash), five (19%) patients in the low-dose radiotherapy group (abdominal pain, diarrhoea, dyspnoea, hypokalemia, and respiratory failure), and four (15%) patients in the hypofractionated group (adrenal insufficiency, colitis, diarrhoea, and hyponatremia). In the low-dose radiotherapy group, there was one death from respiratory failure potentially related to study therapy., Interpretation: Radiotherapy did not increase responses to combined PD-L1 plus CTLA-4 inhibition in patients with NSCLC resistant to PD(L)-1 therapy. However, PD-L1 plus CTLA-4 therapy could be a treatment option for some patients. Future studies should refine predictive biomarkers in this setting., Funding: The US National Institutes of Health and the Dana-Farber Cancer Institute., Competing Interests: Declaration of interests JDS declares research support paid to their institution from Merck, BMS, Regeneron, Debiopharm, and the NCI; consulting or participation on a scientific advisory board, and travel fees and payment for lectures from Genentech, Immunitas, Debiopharm, BMS, Nanobiotix, Tilos, AstraZeneca, LEK, Catenion, ACI Clinical, Astellas, Stimit, and Merck; expert witness fees from Pearson Doyle Mohre and Pastis, Kline and Specter, and Heidell, Pittoni, Murphy and Bach; stock options from Immunitas; and equity in Doximity. SMA declares research support paid to her institution from Merck, Exilixis, Abbvie, Kura Oncology, Amgen, and Nektar. RDG declares support for the present manuscript from a grant from the NCI of the National Institutes of Health (NIH); grants or contracts (to his institution) from Pfizer, Mirati, Daiichi Sankyo, Jounce Therapeutics, Helsinn, BMS, Merck, Janssen, and Takeda; honoraria from Rockpointe CME, Targeted Oncology, OncLive, and the Society for Immunotherapy of Cancer; reimbursement for travel for meetings from Pfizer and AstraZeneca; participation on advisory boards for Mirati, Daiichi Sankyo, AstraZeneca, Sanofi, Oncocyte, Jazz Pharmaceuticals, BluePrint Medicines, and Pfizer; and that he is co-chair of the Hoosier Cancer Research Network Thoracic Clinical Trial Working Group. CL declares honorarium for chairing the data and safety monitoring board for Delcath. JH declares participation on advisory boards for Bayer and Merck, and research funding from Merck, Boston Biomedical, Treos Bio, Senhwa Biosciences, Bayer, Incyte, TriOncology, Seattle Genetics, Hutchison MediPharma, Pionyr Immunotherapeutics, Trovogene, Taiho Pharmaceutical, Effector Therapeutics, and G1 Therapeutics. JLA declares research support from Pfizer; scientific advisory board membership for the Lustgarten Foundation, Stand Up to Cancer, Moleculin Biotech, Bessor Pharma, and Fujifilm; stock options from Bessor Pharma and Moleculin Biotech; and honoraria for data and safety monitoring board membership from Panbela Therapeutics and the Pancreatic Cancer Action Network. SKJ declares grant funding to her institution from the NCI and the Cancer Therapy Evaluation Program, and is a consultant and adjudication committee member for Merck, IMX Medical, and Syntactx. NVU has consulted for QED, Ipsen, Taiho, Incyte, AstraZeneca, and Astellas, and declares research funding from Taiho, Eli Lilly, Ipsen, and EMD Serono, and long position holdings in Natera and Exact Sciences. KLS is a member of the data and safety monitoring committee for the Case Comprehensive Cancer Center. JMJ declares consulting for Foundation Medicine. HP declares research grants or funding to their institution from Adlai Nortye USA, Alpine Immune Sciences, Ambrx, Amgen, Aprea Therapeutics, ArrayBioPharma, Bayer, BeiGene, BJ Bioscience, BMS, Daiichi Pharmaceutical, Eli Lilly, Elicio Therapeutics, EMD Serono, Exelixis, Genentech, Gilead Sciences, GlaxoSmithKline, Gossamer Bio, Hoffman-LaRoche, Hutchison MediPharma, ImmuneOncia Therapeutics, Incyte, Jounce Therapeutics, Mabspace Biosciences, MacroGenics, Medimmune, Medivation, Merck, Millennium, Mirati Therapeutics, Novartis Pharmaceuticals, Oncologie, Pfizer, PsiOxus Therapeutics, Puma Biotechnology, Regeneron Pharmaceuticals, RePare Therapeutics, Seattle Genetics, Synermore Biologics, Taiho Pharmaceutical, TopAlliance Biosciences, TurningPoint Therapeutics, Vedanta Biosciences, and Xencor, and reimbursement for meetings or travel from Daiichi Sankyo and Vedanta. LCV declares consulting fees for Janssen, BMS, Takeda, Jazz, and Daiichi Sankyo. JLW declares research support from the NCI of the NIH. RHM declares research support from ViewRay and AstraZeneca; scientific advisory board participation for ViewRay and AstraZeneca; and expert witness fees from the US Attorney's Office Northern District of New York. MarMA has consulted for Genentech, BMS, Merck, AstraZeneca, Maverick, Blueprint Medicine, Syndax, Ariad/Takeda, Nektar, Gritstone, ArcherDX, Mirati, NextCure, Novartis, EMD Serono, and Panvaxal/NovaRx; declares research funding (to their institute) from AstraZeneca, Lilly, Genentech, BMS, and Merck; and declares participation on a data safety monitoring board and advisory board for BMS and Apollomics. SJR declares research support from BMS, Merck, Affimed, and KITE/Gilead, is on the Scientific Advisory Board of Immunitas Therapeutics, and has equity in Immunitas Therapeutics. AMM declares research support from Merck, BMS, Transgene, Incyte, Trisalus, Genentech, and the NIH; consulting fees from Zosano; advisory board participation for BMS, AstraZeneca, Incyte, and Dynavax; and stock options in MultiplexThera. CJW declares equity in BioNTech, U24 research support from the NCI of the NIH, and research funding from Pharmacyclics. FSH declares research support from the NCI of the NIH, BMS, Novartis, and Genentech; royalties or licenses from BMS and Novartis; consulting fees from BMS, EMD Serono, Surface, Sanofi, Genentech, Gossamer, Trillium, Immunocore, Merck, Novartis, Compass Therapeutics, Pieris, Bioentre, Iovance, Catalym, and Amgen; patents for the methods for treating MHC class I polypeptide-related sequence A disorders (number 20100111973; with royalties paid), tumour antigens and uses thereof (number 7250291; issued), angiopoiten-2 biomarkers predictive of anti-immune checkpoint response (number 20170248603; pending), compositions and methods for the identification, assessment, prevention, and treatment of melanoma using PD-L1 isoforms (number 20160340407; pending), therapeutic peptides (number 20160046716; pending), therapeutic peptides (number 20140004112; pending), therapeutic peptides (number 20170022275; pending), therapeutic peptides (number 20170008962; pending), therapeutic peptides (number 9402905; issued), methods of using pembrolizumab and trebananib (pending), vaccine compositions and methods for restoring NKG2D pathway function against cancers (number 10279021; issued), antibodies that bind to MHC class I polypeptide-related sequence A (number 10106611; issued), and anti-galectin antibody biomarkers predictive of anti-immune checkpoint and anti-angiogenesis responses (number 20170343552; pending); data safety monitoring board and advisory board participation for Aduro and Checkpoint Therapeutics; scientific advisory board leadership for Bicara and Apricity; and stock options in Checkpoint Therapeutics, Pionyr, Apricity, and Bicara. AL is currently an employee of Bristol Myers Squibb. All other authors declare no competing interests., (Copyright © 2022 Elsevier Ltd. All rights reserved.)