Isolated extramedullary relapse after allogeneic bone marrow transplantation for chronic myeloid leukemia.

Relapse of chronic myeloid leukemia (CML) as extramedullary granulocytic sarcoma (GS) after allogeneic bone marrow transplantation (BMT) is a rare occurrence. We report two patients who developed spinal GS as the first indication of relapse after allogeneic BMT for CML. In both cases, the marrow was in morphologic and karyotypic remission. However, fluorescence in situ hybridization (FISH) successfully demonstrated the presence of a minor Ph-positive clone in the marrow, as well as an occult clone with an additional Ph chromosome detected in one case. The results indicated a stronger graft-versus-leukemia effect in the marrow than in the peripheral tissues.