Splenic irradiation for myelofibrosis prior to hematopoietic cell transplantationGagelmann, Nico (Avtor) Hobbs, Gabriela S. (Avtor) Campodonico, Edoardo (Avtor) Helbig, Grzegorz (Avtor) Novak, Polona (Avtor) Schroeder, Thomas (Avtor) Schneider, Artur (Avtor) Rautenberg, Christina (Avtor) Reinhardt, Hans Christian (Avtor) Bosques, Linette (Avtor) aplastic anemiachildrenSplenomegaly is the clinical hallmark of myelofibrosis. Splenomegaly at the time ofallogeneic hematopoietic cell transplantation (HCT) is associated with graft failureand poor graft function. Strategies to reduce spleen size before HCT especially after ailure to Janus kinase (JAK) inhibition represent unmet clinical needs in the field.Here, we leveraged a global collaboration to investigate the safety and efficacy ofsplenic irradiation as part of the HCT platform for patients with myelofibrosis. Weincluded 59 patients, receiving irradiation within a median of 2 weeks (range, 0.9–12 weeks) before HCT. Overall, the median spleen size prior to irradiation was 23 cm(range, 14–35). Splenic irradiation resulted in a significant and rapid spleen size reduc-tion in 97% of patients (57/59), with a median decrease of 5.0 cm (95% confidenceinterval, 4.1–6.3 cm). The most frequent adverse event was thrombocytopenia, withno correlation between irradiation dose and hematological toxicities. The 3-yearoverall survival was 62% (95% CI, 48%–76%) and 1-year non-relapse mortality was26% (95% CI, 14%–38%). Independent predictors for survival were severe thrombo-cytopenia and anemia before irradiation, transplant-specific risk score, higher-intensity conditioning, and present portal vein thrombosis. When using a propensityscore matching adjusted for common confounders, splenic irradiation was associatedwith significantly reduced relapse (p = .01), showing a 3-year incidence of 12% forsplenic irradiation versus 29% for patients with immediate HCT and 38% for patientsreceiving splenectomy. In conclusion, splenic irradiation immediately before HCT is areasonable approach in patients experiencing JAK inhibition failure and is associatedwith a low incidence of relapse20242026-06-03 11:26:41Neznano29693sl