Rasim ŞAHİN, Serdal KORKMAZ, Kerim ERER
Acta Haematologica Oncologica Turcica - 2026;59(1):63-65
Phenotypic conversion between lymphoid and myeloid leukemic lineages is infrequent and generally associated with an unfavorable clinical prognosis. Most reported cases involve relapse of B-cell acute lymphoblastic leukemia (B-ALL) presenting as acute myeloid leukemia (AML). The development of extramedullary disease as myeloid sarcoma after lineage switch, particularly following sequential allogeneic hematopoietic stem cell transplantation (allo-HSCT), is exceedingly rare. A 36-year-old woman with Philadelphia chromosome-positive B-ALL achieved remission after chemotherapy and tyrosine kinase inhibitor-based therapy, but relapsed and underwent two consecutive allo-HSCTs from different donors. Eighteen months after the second transplantation, while in complete remission, she presented with localized knee pain. Imaging and histopathological evaluation confirmed myeloid sarcoma, and bone marrow analysis demonstrated AML, indicating a lineage switch. Treatment with local radiotherapy followed by venetoclax and azacitidine resulted in remission. This case highlights the importance of considering lineage switch in patients with atypical relapse patterns or isolated extramedullary lesions after allo-HSCT.
