ABSTRACT
Isolated extramedullary relapse of acute lymphoblastic leukemia (ALL) after allogeneic bone marrow transplantation (BMT) in the absence of marrow involvement is a rare event, and the mechanisms underlying the selective involvement of extramedullary sites remain undefined. These might be due to relapse in sanctuary sites where the leukemic cells are resistant to preparative regimen, or a stronger graft-versus-leukemia effect in the marrow as compared with peripheral tissues. We report an adult ALL patient who experienced isolated extramedullary relapse in the right pretibial soft tissue and knee joint 42 months after allogeneic BMT. He was treated with localized radiotherapy followed by systemic chemotherapy and donor lymphocyte infusion. After treatment, he is currently well with no evidence of leukemia recurrence for 12 months.