Childhood blastic NK cell leukemia successfully treated with L-asparagenase and allogeneic bone marrow transplantation

Blastic NK cell lymphoma/leukemia is a rare and highly malignant neoplasia in both adults and children. It is characterized by lymphoblastoid morphology without cytoplasmic granules and immature NK cell immunophenotypes (CD56+, CD57-, CD16-). It has predilection for extranodal organ involvement, and the prognosis of affected patients is extremely poor under the current chemotherapy. We present a 14-year-old girl who was diagnosed as having blastic NK cell leukemia with mediastinal, pleural, and pericardial involvement. Immunophenotyping of her leukemic cells showed positive for CD2, CD5, CD7, CD34, CD56, HLA-DR, and cytoplasmic CD3. T cell receptor (TCR) and Immunoglobulin heavy chain genes were not rearranged. She received chemotherapy for acute lymphoblastic leukemia incorporating L-asparaginase (L-asp) which successfully induced complete remission. Bone marrow transplantation (BMT) from her HLA-identical sibling was conducted after two courses of consolidation therapy. Expression of aspargine synthetase (AS) protein in the leukemic cells at diagnosis was examined by an immunocytochemical method. She remains in hematological remission for over 36 months after BMT. The expression of AS protein was negative, suggesting that the leukemic cells were sensitive to L-asp. Induction and consolidation therapy incorporating L-asp followed by allo-BMT might be a promising treatment for child hood blastic NK cell leukemia, but more samples of the rare leukemia need to be studied before any definitive conclusions can be drawn.