This retrospective study evaluated 35 children (median age 5.2 years; range 0.4-18) with myelofibrosis (MF), including 33 with primary myelofibrosis and 2 with secondary myelofibrosis transplanted from matched sibling donor (MSD) (n = 17) or non-MSD (n = 18) between 2000 and 2022. Conditioning was usually chemotherapy-based (n = 33) and myeloablative (n = 32). Fifteen patients received bone marrow (BM), 14 haematopoietic cells (HC) from peripheral blood (PB), and 6 from cord blood (CB). Day +100 acute GvHD II-IV incidence was significantly lower after MSD-haematopoietic cell transplantation (MSD-HCT) than after non-MSD-HCT [18.8% (4.3-41.1) vs 58.8% (31-78.6); p = 0.01]. Six-year non-relapse mortality (NRM) was 18% (7.1-32.8), relapse incidence was 15.9% (5.6-30.9), progression-free survival (PFS) was 66.1% (47-79.7), GvHD-free relapse-free survival was 50% (30.6-66.7), and overall survival (OS) was 71.1% (51.4-84). Six-year PFS and OS were significantly higher after BM transplantation compared to HCT from other sources [85.1% (52.3-96.1) vs 50.8% (26.3-71), p = 0.03, and 90.9% (50.8-98.7) vs 54% (28.1-74.2), p = 0.01, respectively], whereas NRM was significantly lower [0% vs 32% (12.3-53.9); p = 0.02]. This first multicentre study on outcomes of allogeneic HCT in children with myelofibrosis proves feasibility and curative effect of transplantation in these children, suggests that bone marrow transplantation is associated with better outcomes, and indicates the need for further studies.

BMT and Cancer Immunotherapy Department Hadassah Hebrew University Medical Centre Jerusalem Israel

Centre Pierre et Marie Curie Service Hématologie Greffe de Moëlle Alger Algeria

Department and Clinic of Pediatric Oncology Hematology and Bone Marrow Transplantation Wroclaw Medical University Wroclaw Poland

Department Hematology and Bone Marrow Transplant Center Erciyes University Medical School Kayseri Turkey

Department of Blood and Marrow Transplant Royal Manchester Children's Hospital Manchester UK

Department of Bone Marrow Transplantation University of Essen Essen Germany

Department of Haematology Saint Antoine Hospital INSERM UMR 938 Sorbonne University Paris France

Department of Hematology and Stem Cell Transplantation Saint Louis Hospital Paris Cité Université Paris France

Department of Medicine and Surgery Milano Bicocca University Milano Italy

Department of Paediatric Haematology and Stem Cell Transplantation Central Hospital for Southern Pest National Institute for Hematology and Infectology Budapest Hungary

Department of Pediatric Hematology and Oncology King Faisal Specialist Hospital and Research Center Riyadh Saudi Arabia

Department of Pediatric Hematology and Oncology University Hospital Motol Prague Czechia

Department of Pediatric Oncology Hematology and Transplantology University of Medical Sciences Poznan Poland

Department of Pediatrics Division of Pediatric Oncology Stem Cell Transplant University Hospital of Regensburg Regensburg Germany

Department of Pediatrics Jena University Hospital Jena Germany

Department of Pediatrics Pediatric Blood and Marrow Transplantation and Cellular Therapy Program King Hussein Cancer Center Amman Jordan

EBMT Paris Study Office Paris France

Edmond and Lily Safra Children's Hospital Division of Pediatric Hematology Oncology and BMT Sheba Medical Center Tel_Hashomer Israel

Fondazione IME Policlinico Tor Vergata Rome Rome Italy

Great Ormond Street Hospital for Children NHS Foundation Trust London UK

Hematopoietic Stem Cell Transplant Unit Fondazione IRCCS San Gerardo dei Tintori Monza Italy

Hotel Dieu CHU Nantes Dept D'Hematologie Nantes France

King Faisal Specialist Hospital and Research Centre Riyadh Saudi Arabia

Princess Maxima Center University Hospital for Children Stem cell transplantation Utrecht The Netherlands

Robert Debré Hospital and Université de Paris Paris France

Sheffield Children's Hospital Western Bank Sheffield United Kingdom

Unidad de Trasplante Hematopoyético Hospital Niño Jesús Madrid Spain

University Children's Hospital Bratislava Slovakia

University Hospital La Paz Madrid Spain

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