Therapy‐related Ph+ leukemia after both bone marrow and mesenchymal stem cell transplantation for hypophosphatasia

Bone marrow (BM) transplantation (BMT) is one of the treatment strategies for congenital metabolic disease, but leukemia secondary to intensive cytoreductive treatment is a major concern. Besides BM cells, mesenchymal stem cells (MSC) are also used for transplantation. An 8‐month‐old girl with hypophosphatasia underwent transplantation of haploidentical BM cells followed by two transplants of MSC obtained from her father to facilitate osteogenesis. Fludarabine(Flu)/cyclophosphamide (CPA)/anti‐thymocyte globulin were used for myeloablative conditioning, but the patient developed therapy‐related leukemia harboring t(9;22)(q34;q11.2); minor BCR‐ABL (t‐leukemia with Ph) at the age of 32 months. At the age of 40 months she underwent a second BM and third MSC transplant from the same donor. Thereafter, she achieved complete histological and molecular remission. The present case suggests that the combination of cytotoxic agents (Flu/CPA) and MSC led to t‐leukemia with Ph as a consequence of chromosome instability and suppression of host anti‐tumor immunity.