The role of splenic irradiation prior to allogeneic hematopoietic stem transplantation in myelofibrosis: a review of the literature.

Massive splenomegaly in myelofibrosis complicates allogeneic hematopoietic stem-cell transplantation (allo-HSCT) by sequestering donor cells, delaying engraftment, and increasing graft failure risk. Splenic irradiation (SI) offers a non-surgical cytoreductive option when splenectomy is high-risk or JAK-inhibitor response is inadequate. We reviewed published adult series (2000-2024) reporting SI before allo-HSCT. Across nine cohorts ( ~ 200 patients), SI was delivered in fractionated low-to-moderate doses (typically 3-10 Gy) within days to weeks before conditioning. SI reduced spleen size by ~15-53% and was generally well tolerated; hematologic toxicity was expected but manageable. Neutrophil engraftment exceeded 90% in most studies, with platelet engraftment 70-85% and rare primary graft failure. Several cohorts reported overall survival of 60-80% at 2-4 years, and one large analysis suggested lower relapse versus immediate transplant or splenectomy, though findings were heterogeneous and largely retrospective. Platelet recovery can be delayed, particularly in patients with bulky spleens or high-molecular-risk features. Emerging practice favors 5-10 Gy in 5 fractions delivered shortly before conditioning, often alongside ruxolitinib. Prospective studies are needed to standardize dose, timing, and candidate selection. These data support SI as a feasible pre-transplant strategy that facilitates engraftment while avoiding surgical morbidity.