Donor-Derived <i>SF3B1</i>-Mutated Myelodysplastic Neoplasm/Syndrome.

We report a rare case of donor-derived <i>SF3B1</i>-mutated myelodysplastic syndrome (MDS) arising in a 45-year-old woman following haploidentical allogeneic hematopoietic stem cell transplantation (allo-HSCT) for acute myeloid leukemia. Initial remission was achieved post-induction, and transplantation resulted in full donor chimerism. However, routine post-transplant surveillance revealed a novel <i>SF3B1</i> K666N mutation, evolving to overt MDS with ring sideroblasts and multilineage dysplasia. Persistent 100% donor chimerism confirmed the donor-derived nature of the neoplasm. The patient's course was complicated by severe graft-versus-host disease, opportunistic infections, and ultimately death. This case highlights the diagnostic challenges and clinical implications of donor-derived MDS, particularly involving <i>SF3B1</i> mutations, which are typically associated with favorable prognosis but remain poorly characterized in post-transplant settings.