Recurrent extramedullary relapse of acute myelogenous leukemia after allogeneic hematopoietic stem cell transplantation in a patient with the chromosomal abnormality t(8;21) and CD56-positivity.

Isolated extramedullary (EM) relapse of acute myelogenous leukemia (AML) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is rare. Predisposing factors include CD56 expression and the chromosomal abnormality t(8;21). We describe an AML patient showing the chromosomal abnormality t(8;21) and CD56 expression who experienced a unique EM relapse after allo-HSCT. Approximately 10 months after allo-HSCT, he experienced relapse involving the femur and lumbar vertebrae and, subsequently, an EM relapse of the stomach. Although we administered only local radiotherapy and not systemic chemotherapy, he showed no bone marrow relapse on long-term follow-up after achieving complete hematological remission. These findings suggest that the graft-versus-leukemia effect may preferentially maintain marrow remission rather than prevent EM relapse. In addition, our findings show that extended survival is possible after EM relapse following allo-HSCT in patients with marrow hematopoiesis of donor origin, and that augmentation of the graft-versus-leukemia effect may be useful.