The NFIA::CBFA2T3 identifies a molecularly defined subgroup of acute erythroid leukemia/erythroid sarcoma

Introduction The World Health Organization classification of tumors of hematopoietic and lymphoid tissues recognizes acute erythroid leukemia as a distinct entity under myeloid neoplasms. Erythroblastic sarcoma, also known as extramedullary erythroid sarcoma, is defined as a rare extramedullary tumor composed of erythroid precursors, typically occurring outside the bone marrow. While both entities involve immature erythroid precursors and share similar histology, acute erythroid leukemia is a systemic marrow-based leukemia, whereas erythroblastic sarcoma is a localized mass-forming lesion. Since these entities can overlap morphologically with other clinically distinct myeloid malignancies and myelodysplastic syndrome, it is fundamental to characterize them genetically. Materials and methods We report a rare and diagnostic challenging case of a 2-year-old boy with erythroid sarcoma characterized by extensive extramedullary involvement, including mediastinum, gastrointestinal tract, pleura/peritoneum, bilateral kidneys, and lymph nodes. Results and discussion The patient achieved a sustained complete remission following standard acute myeloid leukemia-like therapy with consolidative allogenic stem cell transplant. An NFIA::CBFA2T3 chimeric fusion was found in the tumor genome. Since such a fusion transcript has been identified only in cases of pediatric erythroleukemia/erythroid sarcomas, we propose that it may characterize a molecularly defined subgroup of leukemias. The patient is in full remission with no signs of graft-versus-host disease twenty-eight months after the transplant.