Purpose: Allogeneic hematopoietic cell transplantation (HCT) is the only potentially curative therapy for myelodysplastic syndromes (MDS), although it is infrequently offered to older patients. The relative benefits of HCT over non-HCT therapy in older patients with higher-risk MDS have not been defined., Methods: We conducted a multicenter biologic assignment trial comparing reduced-intensity HCT to hypomethylating therapy or best supportive care in subjects 50-75 years of age with intermediate-2 or high-risk de novo MDS. The primary outcome was overall survival probability at 3 years. Between January 2014 and November 2018, we enrolled 384 subjects at 34 centers. Subjects were assigned to the Donor or No-Donor arms according to the availability of a matched donor within 90 days of study registration., Results: The median follow-up time for surviving subjects was 34.2 months (range: 2.3-38 months) in the Donor arm and 26.9 months (range: 2.4-37.2 months) in the No-Donor arm. In an intention-to-treat analysis, the adjusted overall survival rate at 3 years in the Donor arm was 47.9% (95% CI, 41.3 to 54.1) compared with 26.6% (95% CI, 18.4 to 35.6) in the No-Donor arm ( P = .0001) with an absolute difference of 21.3% (95% CI, 10.2 to 31.8). Leukemia-free survival at 3 years was greater in the Donor arm (35.8%; 95% CI, 29.8 to 41.8) compared with the No-Donor arm (20.6%; 95% CI, 13.3 to 29.1; P = .003). The survival benefit was seen across all subgroups examined., Conclusion: We observed a significant survival advantage in older subjects with higher-risk MDS who have a matched donor identified and underwent reduced-intensity HCT, when compared with those without a donor. HCT should be included as an integral part of MDS management plans in fit older adults with higher-risk MDS., Competing Interests: Ryotaro NakamuraConsulting or Advisory Role: Viracor Eurofins, Magenta Therapeutics, Kadmon, Napajen PharmaResearch Funding: Helocyte, Miyarisan PharmaceuticalTravel, Accommodations, Expenses: Kyowa Hakko Kirin, Alexion Pharmaceuticals Bart ScottHonoraria: Bristol Myers SquibbConsulting or Advisory Role: Celgene, Acceleron Pharma, Astex Pharmaceuticals, NovartisSpeakers' Bureau: Alexion Pharmaceuticals, Celgene, Jazz Pharmaceuticals, NovartisResearch Funding: Celgene Betul OranResearch Funding: AROG Phamarceuticals, Astex Pharmaceuticals Asmita MishraResearch Funding: Novartis Richard T. MaziarzHonoraria: Novartis, Omeros, PACT PharmaceuticalsConsulting or Advisory Role: Novartis, Incyte, Kite, a Gilead company, Bristol Myers Squibb, Intellia Therapeutics, ArtivaPatents, Royalties, Other Intellectual Property: Athersys Inc shared patent re: use of mesenchymal stromal cells for treatment of GVHDTravel, Accommodations, Expenses: Novartis, Incyte, Kite, a Gilead company Joseph McGuirkHonoraria: Kite, a Gilead company, AlloVir, Juno Therapeutics, Magenta TherapeuticsConsulting or Advisory Role: Kite, a Gilead company, Juno Therapeutics, AlloVir, Magenta Therapeutics, EcoR1 CapitalSpeakers' Bureau: Kite/GileadResearch Funding: Novartis, Fresenius Biotech, Astellas Pharma, Bellicum Pharmaceuticals, Gamida Cell, Pluristem Therapeutics, Kite, a Gilead company, AlloVirTravel, Accommodations, Expenses: Kite, a Gilead company Peter WesterveltConsulting or Advisory Role: Pfizer Sumithira VasuConsulting or Advisory Role: Omeros, Johnson & JohnsonPatents, Royalties, Other Intellectual Property: The Ohio State University has entered into an exclusive licensing agreement with Kiadis Inc Mrinal PatnaikHonoraria: Kura OncologyConsulting or Advisory Role: Kura OncologyResearch Funding: Stemline Therapeutics Stephen J. FormanStock and Other Ownership Interests: MustangBio, Lixte BiotechnologyConsulting or Advisory Role: Alimera Sciences, Lixte Biotechnology, MustangBioResearch Funding: MustangBioPatents, Royalties, Other Intellectual Property: MustangBio Mikkael A. SekeresConsulting or Advisory Role: Celgene, Millennium, Pfizer, NovartisResearch Funding: Takeda, Pfizer, Bristol Myers Squibb Frederick AppelbaumStock and Other Ownership Interests: Jasper Therapeutics Brent LoganConsulting or Advisory Role: Daiichi Sankyo, Enlivex Therapeutics Ltd, Gamida Cell Mary HorowitzConsulting or Advisory Role: Magenta Therapeutics, Janssen Research & Development, MedacResearch Funding: Biovitrum, Jazz Pharmaceuticals, Magenta Therapeutics, Novartis, Kite/Gilead, Actinium Pharmaceuticals, Amgen, Amneal Pharmaceuticals, Anthem, Bluebird Bio, Bristol Myers Squibb, Chimerix, CSL Behring, Cyto-Sen Therapeutics, Daiichi Sankyo, Gamida Cell, GlaxoSmithKline, Mesoblast, Miltenyi Biotec, Neovii, Oncoimmune, Pfizer, Pharmacyclics, Regeneron, Sanofi, Seattle Genetics, Shire Corey CutlerStock and Other Ownership Interests: Bluebird Bio, Idera, Verastem, Northwest Biotherapeutics, Actinium PharmaceuticalsHonoraria: Omeros, PfizerConsulting or Advisory Role: Incyte, Jazz Pharmaceuticals, CareDX, Mesoblast, Syndax, MedsenicNo other potential conflicts of interest were reported.