Gemtuzumab ozogamicin therapy for isolated extramedullary AML relapse after allogeneic hematopoietic stem-cell transplantation.

The treatment of isolated extramedullary relapse (IEMR) after allogeneic hematopoietic stem-cell transplantation (allo-HSCT) poses a challenge for which no standard approach exists. Gemtuzumab ozogamicin (GO) is a recombinant humanized monoclonal antibody, conjugated to calicheamicin, which targets the CD33 antigen that is expressed in acute myelogenous leukemia (AML) blasts. The selectivity of GO for CD33-positive leukemic cells makes it an attractive agent for use in patients with multiple sites of IEMR after allo-HSCT, because GO does not suppress cells responsible for the putative graft-versus-leukemia (GVL) effect. Herein, we describe a 54-year-old male patient who developed AML with multiple sites of extramedullary (EM) relapse after allo-HSCT, and who exhibited apparent donor-derived hematopoiesis in the bone marrow. At approximately 120 days after allo-HSCT, the patient complained of severe lumbago. T2-weighted magnetic resonance images and fluorodeoxyglucose-positron emission tomography showed multiple mass lesions in soft tissue and bone. A biopsy specimen from a lumbar soft tissue mass confirmed EM relapse, and revealed that donor T lymphocytes were present in the relapse site and that leukemic cells expressed CD33. Therefore, to maintain the GVL effect of donor T lymphocytes, the patient was treated with GO as a single agent. He achieved complete hematological remission, and has remained in remission, with only mild liver injury, for more than 10 months since GO treatment. GO can be an effective therapy for IEMR after allo-HSCT, especially when cytotoxic T lymphocytes react to leukemic cells at the site of EM relapse.