Summary:The optimal treatment for natural killer (NK) cell leukemia after chronic active Epstein-Barr virus (CAEBV) infection has not been determined. A 15-yearold boy presented with NK cell leukemia following CAEBV infection for 5 years. The peripheral blood and BM had an increased number of CD3 À CD56 + large granular lymphocytes and a monoclonal integration of the EBV genome was detected. Chemotherapy was not sufficiently effective to control the disease. Allogeneic BMT from an HLA-identical sister was performed using a conditioning regimen consisting of total body irradiation, cyclophosphamide and thiotepa. The patient is diseasefree with a perfect performance status 24 months after BMT. This is the first report to show that allogeneic BMT is potentially able to cure NK cell leukemia after CAEBV infection.

Viral infection may be present in two thirds of children with newly diagnosed JMML, but it does not constitute a basis for revising clinical management. The possibility that EBV or other viruses contribute to JMML pathogenesis by stimulating pre-exiting malignant clones warrants further investigation.