Background: Adding ibrutinib to standard immunochemotherapy might improve outcomes and challenge autologous stem-cell transplantation (ASCT) in younger (aged 65 years or younger) mantle cell lymphoma patients. This trial aimed to investigate whether the addition of ibrutinib results in a superior clinical outcome compared with the pre-trial immunochemotherapy standard with ASCT or an ibrutinib-containing treatment without ASCT. We also investigated whether standard treatment with ASCT is superior to a treatment adding ibrutinib but without ASCT., Methods: The open-label, randomised, three-arm, parallel-group, superiority TRIANGLE trial was performed in 165 secondary or tertiary clinical centres in 13 European countries and Israel. Patients with previously untreated, stage II-IV mantle cell lymphoma, aged 18-65 years and suitable for ASCT were randomly assigned 1:1:1 to control group A or experimental groups A+I or I, stratified by study group and mantle cell lymphoma international prognostic index risk groups. Treatment in group A consisted of six alternating cycles of R-CHOP (intravenous rituximab 375 mg/m 2 on day 0 or 1, intravenous cyclophosphamide 750 mg/m 2 on day 1, intravenous doxorubicin 50 mg/m 2 on day 1, intravenous vincristine 1·4 mg/m 2 on day 1, and oral prednisone 100 mg on days 1-5) and R-DHAP (or R-DHAOx, intravenous rituximab 375 mg/m 2 on day 0 or 1, intravenous or oral dexamethasone 40 mg on days 1-4, intravenous cytarabine 2 × 2 g/m 2 for 3 h every 12 h on day 2, and intravenous cisplatin 100 mg/m 2 over 24 h on day 1 or alternatively intravenous oxaliplatin 130 mg/m 2 on day 1) followed by ASCT. In group A+I, ibrutinib (560 mg orally each day) was added on days 1-19 of R-CHOP cycles and as fixed-duration maintenance (560 mg orally each day for 2 years) after ASCT. In group I, ibrutinib was given the same way as in group A+I, but ASCT was omitted. Three pairwise one-sided log-rank tests for the primary outcome of failure-free survival were statistically monitored. The primary analysis was done by intention-to-treat. Adverse events were evaluated by treatment period among patients who started the respective treatment. This ongoing trial is registered with ClinicalTrials.gov, NCT02858258., Findings: Between July 29, 2016 and Dec 28, 2020, 870 patients (662 men, 208 women) were randomly assigned to group A (n=288), group A+I (n=292), and group I (n=290). After 31 months median follow-up, group A+I was superior to group A with 3-year failure-free survival of 88% (95% CI 84-92) versus 72% (67-79; hazard ratio 0·52 [one-sided 98·3% CI 0-0·86]; one-sided p=0·0008). Superiority of group A over group I was not shown with 3-year failure-free survival 72% (67-79) versus 86% (82-91; hazard ratio 1·77 [one-sided 98·3% CI 0-3·76]; one-sided p=0·9979). The comparison of group A+I versus group I is ongoing. There were no relevant differences in grade 3-5 adverse events during induction or ASCT between patients treated with R-CHOP/R-DHAP or ibrutinib combined with R-CHOP/R-DHAP. During maintenance or follow-up, substantially more grade 3-5 haematological adverse events and infections were reported after ASCT plus ibrutinib (group A+I; haematological: 114 [50%] of 231 patients; infections: 58 [25%] of 231; fatal infections: two [1%] of 231) compared with ibrutinib only (group I; haematological: 74 [28%] of 269; infections: 52 [19%] of 269; fatal infections: two [1%] of 269) or after ASCT (group A; haematological: 51 [21%] of 238; infections: 32 [13%] of 238; fatal infections: three [1%] of 238)., Interpretation: Adding ibrutinib to first-line treatment resulted in superior efficacy in younger mantle cell lymphoma patients with increased toxicity when given after ASCT. Adding ibrutinib during induction and as maintenance should be part of first-line treatment of younger mantle cell lymphoma patients. Whether ASCT adds to an ibrutinib-containing regimen is not yet determined., Funding: Janssen and Leukemia & Lymphoma Society., Competing Interests: Declaration of interests MD reports research grants for clinical studies from AbbVie, Bayer, Bristol-Myers Squibb/Celgene, Gilead/Kite, Janssen, and Roche; speakers' honoraria from AstraZeneca, BeiGene, Gilead/Kite, Janssen, Lilly, Novartis, and Roche; travel support from Janssen and Roche; and participation on a Data Safety Monitoring Board or Advisory Board for AbbVie, AstraZeneca, BeiGene, Bristol-Myers Squibb/Celgene, Gilead/Kite, Janssen, Lilly/Loxo Oncology, Novartis, and Roche. JDo reports payment for expert testimony (once Advisory Board) from Lilly. EG reports grants from Janssen; honoraria (educational lecture) from Genmab, Gilead, Janssen, and Lilly; support for attending meetings or travel from Janssen and Roche; and participation on a Data Safety Monitoring Board or Advisory Board for Gilead/Kite and Miltenyi Biotec. MJ reports payment or honoraria for lectures, presentations, speakers' bureaus, manuscript writing, or educational events from AbbVie, Gilead/Kite, and Roche; participation on a Data Safety Monitoring Board or Advisory Board for AbbVie, Gilead/Kite, Janssen, and Pierre Fabre. JW reports grants to his institution from GlaxoSmithKline/Novartis and Roche; honoraria for lectures from AbbVie, Amgen, Gilead, Novartis, Roche, Servier, and Takeda; participation on an Advisory Board from AbbVie, Gilead, Novartis, Roche, and Takeda. MHu reports payment or honoraria for lectures, presentations, speakers' bureaus, manuscript writing, or educational events from AbbVie, AstraZeneca, Celgene, Genmab, Janssen, Merck, Roche, and Takeda; participation on a Data Safety Monitoring Board or Advisory Board for AbbVie, AstraZeneca, Celgene, Genmab, Janssen, Merck, Roche, and Takeda. UM reports travel support from Amgen, Bristol-Myers Squibb/Celgene, Gilead, Janssen-Cilag, and Roche; Advisory Board role for Amgen, AstraZeneca, BeiGene, Bristol-Myers Squibb/Celgene, Gilead, Incyte, Janssen-Cilag, Novartis, Pfizer, Roche, Sanofi, and Takeda; participation in national Guideline committee for the German-Swiss-Austrian Guideline for Mantle Cell Lymphoma. JR reports participation on an Advisory Board for AstraZeneca. VV reports consulting fees from AbbVie, BeiGene, Gilead, Lilly, and Roche; payment or honoraria for lectures, presentations, speakers' bureaus, manuscript writing, or educational events from Janssen; payment for expert testimony from Gilead and Roche; support for attending meetings or travel from AbbVie and Gilead. MGdS reports a research grant from AstraZeneca; payment for Advisory Boards from AbbVie, Gilead, Janssen-Cilag, Roche, and Takeda; payment or honoraria for educational events from Gilead and Janssen-Cilag; support for attending meetings or travel from AbbVie, Janssen-Cilag, Roche, and Takeda; participation on a Data Safety Monitoring Board or Advisory Board for Roche; leadership in a scientific society (Sociedade Portuguesa de Hematologia); administration board on a patient advocacy group (Associação Portuguesa Contra a Leucemia). SL reports grants or contracts to her institution from Bristol-Myers Squibb/Celgene, Genmab, HUTCHMED, Novartis, and Roche; consulting fees from AbbVie, Genmab, Gilead, Novartis, ORION Pharma, Roche, and Swedish Orphan Biovitrum (sobi); payment or honoraria for lectures, presentations, speakers' bureaus, manuscript writing, or educational events from Gilead, Incyte, and Novartis; participation on a Data Safety Monitoring Board or Advisory Board for Incyte. StS reports grants or contracts from any entity from AbbVie, Acerta Pharma, Amgen, AstraZeneca, BeiGene, Bristol-Myers Squibb/Celgene, Roche, Gilead, GlaxoSmithKline, Infinity Pharmaceuticals, Janssen, Novartis, Sunesis Pharmaceuticals, and Verastem; consulting fees from AbbVie, Acerta Pharma, Amgen, AstraZeneca, BeiGene, Bristol-Myers Squibb/Celgene, Roche, Gilead, GlaxoSmithKline, Infinity Pharmaceuticals, Janssen, Novartis, Sunesis Pharmaceuticals, and Verastem; payment or honoraria for lectures, presentations, speakers' bureaus, manuscript writing, or educational events from AbbVie, Acerta Pharma, Amgen, AstraZeneca, BeiGene, Bristol-Myers Squibb/Celgene, Roche, Gilead, GlaxoSmithKline, Infinity Pharmaceuticals, Janssen, Novartis, Sunesis Pharmaceuticals, and Verastem; support for attending meetings or travel from AbbVie, Acerta Pharma, Amgen, AstraZeneca, BeiGene, Bristol-Myers Squibb/Celgene, Roche, Gilead, GlaxoSmithKline, Infinity Pharmaceuticals, Janssen, Novartis, Sunesis Pharmaceuticals, and Verastem; participation on a Data Safety Monitoring Board or Advisory Board for AbbVie, Acerta Pharma, Amgen, AstraZeneca, BeiGene, Bristol-Myers Squibb/Celgene, Roche, Gilead, GlaxoSmithKline, Infinity Pharmaceuticals, Janssen, Novartis, Sunesis Pharmaceuticals, and Verastem; receipt of equipment, materials, drugs, medical writing, gifts, or other services from AbbVie, Acerta Pharma, Amgen, AstraZeneca, BeiGene, Bristol-Myers Squibb/Celgene, Roche, Gilead, GlaxoSmithKline, Infinity Pharmaceuticals, Janssen, Novartis, Sunesis Pharmaceuticals, and Verastem. AK reports payment or honoraria for lectures, presentations, speakers' bureaus, manuscript writing, or educational events from AbbVie, Bristol-Myers Squibb/Celgene, Novartis, Roche, Swedish Orphan Biovitrum (sobi), and Takeda; support for attending meetings or travel from AbbVie, BeiGene, EUSA Pharma, Swedish Orphan Biovitrum (sobi), and Takeda. RJ reports travel support for meeting attendance from BeiGene; meeting fee from Janssen. GH reports grants or contracts for clinical research from AbbVie, Gilead/Kite, Incyte, Janssen, MorphoSys, Pfizer, and Roche; consulting fees from AbbVie, ADC Therapeutics, AstraZeneca, Bristol-Myers Squibb, Genmab, Gilead/Kite, Incyte, Janssen, Lilly, Miltenyi Biotec, Novartis, and Roche; payment or honoraria for lectures, presentations, speakers' bureaus, manuscript writing, or educational events from AbbVie, AstraZeneca, BeiGene, Bristol-Myers Squibb, Genmab, Gilead, Incyte, Janssen, Lilly, and Roche; support for attending meetings or travel from Gilead/Kite and Janssen; participation on a Data Safety Monitoring Board or Advisory Board for Miltenyi Biotec. CV reports payment or honoraria for lectures, presentations, speakers' bureaus, manuscript writing, or educational events from AbbVie, AstraZeneca, BeiGene, Bristol-Myers Squibb, Gilead/Kite, Incyte, Istituto Gentili, Janssen, Lilly, Novartis, Pfizer, Roche, and Servier; participation on a Data Safety Monitoring Board or Advisory Board for AbbVie, Bristol-Myers Squibb, Incyte, Janssen, Lilly, Pfizer, and Roche. TvM reports payment or honoraria for educational lectures from Bristol-Myers Squibb/Celgene, Gilead/Kite, Janssen, and Lilly; participation on a Data Safety Monitoring Board or Advisory Board for GE HealthCare and Gilead/Kite. SW reports payment to his institution from AbbVie, Stemline Therapeutics, and Takeda; payment for expert testimony from Stemline Therapeutics; support for attending meetings or travel from AbbVie and BeiGene; participation on a Data Safety Monitoring Board or Advisory Board for AbbVie, Astra Zeneca, Roche, and Stemline Therapeutics. PLZ reports payment or honoraria for lectures, presentations, speakers' bureaus, manuscript writing, or educational events from AstraZeneca, BeiGene, Bristol-Myers Squibb, Gilead, Incyte, Janssen, Kyowa Kirin, Merck Sharp and Dohme, Novartis, Roche, Swedish Orphan Biovitrum (sobi), and Takeda; participation on a Data Safety Monitoring Board or Advisory Board for AstraZeneca, BeiGene, Bristol-Myers Squibb, Gilead, Incyte, Janssen, Kyowa Kirin, Merck Sharp and Dohme, Novartis, Roche, Swedish Orphan Biovitrum (sobi), and Takeda. UN reports consulting fees to his institution from AstraZeneca, BeiGene, Bristol-Myers Squibb/Celgene, Gilead, Incyte, Janssen-Cilag, Kyowa Kirin, Novartis, Pierre Fabre, Roche, and Takeda; payment or honoraria for lectures, presentations, speakers' bureaus, manuscript writing, or educational events to his institution from Bristol-Myers Squibb/Celgene, Gilead, Novartis, and Takeda; support for attending meetings or travel from Janssen, Gilead, Roche, and Takeda; participation on a Data Safety Monitoring Board or Advisory Board for AstraZeneca, BeiGene, Bristol-Myers Squibb/Celgene, Gilead, Incyte, Janssen-Cilag, Kyowa Kirin, Novartis, Pierre Fabre, Roche, and Takeda. CH reports payment or honoraria for lectures, presentations, speakers' bureaus, manuscript writing, or educational events from Bristol-Myers Squibb, Janssen, and Pfizer; support for attending meetings or travel from AbbVie and Janssen. MHa reports payment or honoraria for lectures, presentations, speakers' bureaus, manuscript writing, or educational events from Falk Foundation, Gilead, Novartis, and Swedish Orphan Biovitrum (sobi); payment for expert testimony from Amgen, Bristol-Myers Squibb/Celgene, Gilead, Incyte, Janssen, Novartis, Pizer, Roche, Sanofi-Aventis, and Swedish Orphan Biovitrum (sobi). WK reports research grants provided to his institution from Amgen, Janssen, Roche, and Takeda. DG reports support for attending meetings and travel from Janssen. CS reports consulting fees from Bristol-Myers Squibb and Janssen; payment or honoraria for lectures, presentations, speakers' bureaus, manuscript writing, or educational events from AstraZeneca and Bristol-Myers Squibb; support for attending meetings or travel from Gilead/Kite. MU reports institutional funding of the TRIANGLE trial from Janssen. ML reports consulting fees from AstraZeneca, BeiGene, Janssen, and Lilly; honoraria for lectures, presentations, speakers' bureaus, manuscript writing, or educational events from AstraZeneca, BeiGene, Janssen, and Lilly; participation on a Data Safety Monitoring Board with Acerta. All other authors (MT, OS, LJ, MC, LA, PH, FB, KS, JDi, CP, and EH) declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license. Published by Elsevier Ltd.. All rights reserved.)