Pediatric acute blastic natural killer cell leukemia.

The goal of this report is to describe a rare case of pediatric blastic natural killer (NK) cell leukemia and to compare pediatric blastic NK cell leukemia/lymphoma to other reported cases of pediatric NK cell leukemia. The patient, a 9-year-old girl, presented with acute leukemia with a phenotype similar to adult blastic NK cell leukemia/lymphoma. The blasts were agranular and expressed CD7, 45, 56, and HLA-DR, but not CD3, 11c, 13, 33, or TdT. She had a complete response to ALL-directed chemotherapy, but had multiple relapses involving the cerebrospinal fluid, nasal sinus, lymph node and skin. In addition to the reported case, a review of the literature identified 9 previously reported cases of NK cell leukemia in patients 18 years of age or less. Cases were subdivided into blastic, acute/aggressive, and myeloid precursor NK cell leukemia based upon CD13/33 expression and morphologic characteristics. Compared to pediatric acute/aggressive NK cell leukemia, children with blastic NK cell leukemia showed greater variation in age and race. Prognosis was poor for all groups. Pediatric blastic NK cell leukemia is a distinct clinicopathologic entity which differs from other types of pediatric NK cell leukemia.