Background: This phase 1b/2 PCYC-1123-CA study evaluated efficacy and safety of the combination of ibrutinib, lenalidomide, and rituximab (iR 2 regimen) in patients with relapsed/refractory diffuse large B-cell lymphoma (DLBCL) ineligible for stem cell transplantation., Methods: In phase 2, patients with relapsed/refractory non-germinal centre B-cell-like DLBCL received oral ibrutinib 560 mg once daily and oral lenalidomide 20 mg or 25 mg once daily on Days 1-21 of each 28-day cycle until disease progression or unacceptable toxicity and intravenous rituximab 375 mg/m 2 on Day 1 of Cycles 1-6. The primary endpoint was overall response rate (ORR) in the response-evaluable population (received any study treatment and had ≥1 post-baseline disease assessment). The study was done at 24 academic and community hospitals in Belgium, Germany, United Kingdom, and USA. This study was registered with ClinicalTrials.gov, NCT02077166., Findings: Between March 13, 2014 and October 2, 2018, 89 patients were enrolled with a median time on study of 35.0 months. Best ORR in the response-evaluable population (n = 85) was 49% (95% confidence interval [CI], 38-61) across dose cohorts and 53% (95% CI, 39-67) and 44% (95% CI, 26-62) in the 20 mg and 25 mg lenalidomide cohorts, respectively, with complete responses in 24/85 (28%), 17/53 (32%), and 7/32 (22%) patients, respectively. Grade 3/4 adverse events (AEs) occurred in 81/89 patients (91%), most frequently neutropenia (36/89; 40%), maculopapular rash (16/89; 18%), anaemia (12/89; 13%), and diarrhoea (9/89; 10%). Serious adverse events occurred in 57/89 patients (64%). Fatal AEs occurred in 12/89 patients (13%); causes of death were worsening of DLBCL (n = 7), pneumonia (n = 3), sepsis (n = 1), and cardiac arrest (n = 1)., Interpretation: The most frequent AEs (diarrhoea, neutropenia, fatigue, cough, anaemia, peripheral oedema, and maculopapular rash) were consistent with known safety profiles of the individual drugs. The iR 2 regimen demonstrated antitumour activity with durable responses in patients with relapsed/refractory DLBCL., Funding: Pharmacyclics LLC, an AbbVie Company., Competing Interests: R.R. reports a consulting/advisory role with Pharmacyclics LLC, an AbbVie Company; and research funding from Janssen and Pharmacyclics LLC, an AbbVie Company. P.J. reports honoraria from Bristol-Myers Squibb, Genmab, Incyte, Kymera, MorphoSys, Novartis, and Takeda; a consulting/advisory role for Epizyme and Janssen; and patents/royalties/other intellectual property with the University of Southampton. N.G. reports a consulting/advisory role for AbbVie, ADC Therapeutics, Adaptive Biotech, BeiGene, Bristol Myers Squibb, Genmab, Gilead/Kite, Incyte, Janssen, TG Therapeutics, and Pharmacyclics LLC, an AbbVie Company; research funding from Bristol Myers Squibb, Genentech, TG Therapeutics, and Pharmacyclics LLC, an AbbVie Company; and speakers bureau for AbbVie, Bristol Myers Squibb, Epizyme, Gilead/Kite, Janssen, and Pharmacyclics LLC, an AbbVie Company. JRu reports a consulting/advisory role for Celgene/Bristol Myers Squibb, Daiichi Sankyo, Kite Pharma, Seagen, and Secura Bio; and research funding from AstraZeneca, Celgene/Bristol Myers Squibb, Daiichi Sankyo, and Genentech. K.M.A. reports honoraria from and a consulting/advisory role for BeiGene, Celgene, Gilead, Novartis, and Roche; research funding from ADC Therapeutics, Autolus, Bristol Myers Squibb, Janssen, Novartis, and Pharmacyclics LLC, an AbbVie Company; and travel/accommodations/expenses from Celgene, Gilead, Novartis, and Roche. R.J. reports honoraria from Gilead and Novartis; and a consulting/advisory role for Gilead, Novartis, and Takeda. G.V., S.d.V., S.K., and F.O. have nothing to disclose. D.C. reports a consulting/advisory role with OVIBIO; and research funding from 4SC, Bayer, Celgene, Clovis, Eli Lilly, Leap, MedImmune/AstraZeneca, the National Institute for Health and Care Research Efficacy and Mechanism Evaluation Programme, and Roche. L.F. reports honoraria from and a consulting/advisory role for EUSA Pharma; and research funding from Pharmacyclics LLC, an AbbVie Company. J.Ra. reports stock or other ownership with ADC Therapeutics (self) and AstraZeneca (spouse); honoraria from ADC Therapeutics, Bristol Myers Squibb, and Takeda; a consulting/advisory role and speakers bureau for ADC Therapeutics and Takeda; and research funding from Takeda. S.B. reports a consulting/advisory role for and travel/accommodations/expenses from AbbVie, Gilead, Janssen, Roche, and Takeda. D.M. reports stock or other ownership with Johnson & Johnson, Merck, Pfizer, Regeneron, Roche, and Vertex Pharma. J.M. reports honoraria from Curio, Kyowa, OneView, Physicians' Education Resource, Seagen, and Targeted Oncology; a consulting/advisory role for ADC Therapeutics, Alexion, Bayer, BeiGene, Bristol Myers Squibb, Debiopharm, Epizyme, Fosun Kite, Genmab, Gilead/Kite Pharma, Innovent, Janssen, Juno/Celgene, Kyowa, Karyopharm, Morphosys/Incyte, Novartis, Pfizer, Seagen, Servier, and Pharmacyclics LLC, an AbbVie Company; research funding from Bayer, Celgene, Genentech, Gilead/Kite Pharma, Incyte, Janssen, Merck, Millennium, Portola, Seagen, and Pharmacyclics LLC, an AbbVie Company; and speakers bureau for Acrotech/Aurobindo, AstraZeneca, Bayer, BeiGene, Celgene/Bristol Myers Squibb, Genentech/Roche, Gilead/Kite Pharma, Janssen, Kyowa, Seagen, Verastem, and Pharmacyclics LLC, an AbbVie Company. J.P. reports employment and stock or other ownership with AbbVie. E.S.-G. reports employment and stock or other ownership with AbbVie. K.E. reports employment with Pharmacyclics LLC, an AbbVie Company; and stock or other ownership with AbbVie. J.K.N. reports employment and stock or other ownership with AbbVie. A.G. reports a leadership position with COTA Healthcare, Genomic Testing Cooperative LCA, and Resilience; stock or other ownership with Alloplex, COTA Healthcare, Genomic Testing Cooperative LCA, Resilience, and Vincerx; a consulting/advisory role for Alloplex, AstraZeneca, Bristol Myers Squibb, Celgene, Clinical Advances H&O, Elsevier's Practice Update Oncology, Gilead, Hoffmann-La Roche, Janssen, Kite Pharma, Medscape, Michael J Hennessey Associates, MorphoSys, Novartis, Onclive Peer Exchange, Physicians Education Resource, Roswell Park, Vincerx, and Xcenda-Amerisource; research funding from Acerta, AstraZeneca, Bristol Myers Squibb, Genentech, Hoffmann-La Roche, Infinity, Janssen, Karyopharm, Kite Pharma, MorphoSys, Seagen, Verastem, and Pharmacyclics LLC, an AbbVie Company; travel/accommodations/expenses from Alloplex, AstraZeneca, Bristol Myers Squibb, Celgene, Clinical Advances H&O, COTA Healthcare, Elsevier's Practice Update Oncology, Genomic Testing Cooperative LCA, Gilead, Hoffmann-La Roche, Janssen, Kite Pharma, Medscape, Michael J Hennessey Associates, MorphoSys, Novartis, Onclive Peer Exchange, Physicians Education Resource, Roswell Park, Resilience, Vincerx, and Xcenda-Amerisource; and other relationship with Acerta, Alloplex, AstraZeneca, Bristol Myers Squibb, Celgene, Clinical Advances H&O, COTA Healthcare, Elsevier's Practice Update Oncology, Genentech, Genomic Testing Cooperative LCA, Gilead, Hoffmann-La Roche, Infinity, Janssen, Karyopharm, Kite Pharma, Medscape, Michael J Hennessey Associates, MorphoSys, Novartis, Onclive Peer Exchange, Physicians Education Resource, Resilience, Roswell Park, Seagen, Verastem, Vincerx, Xcenda-Amerisource, and Pharmacyclics LLC, an AbbVie Company., (© 2022 The Authors.)