Therapy‐related P h+ 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. F ludarabine( F lu)/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 P h) 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 ( F lu/ CPA ) and MSC led to t‐leukemia with P h as a consequence of chromosome instability and suppression of host anti‐tumor immunity.