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Recognition of unusual presentation of natural killer cell leukemia

Expansion of the natural killer (NK) subset of lymphocytes represents a rare leukemia phenotype with variations in clinical presentation, morphology, surface phenotype, and effector function. This paper reports on a 5‐year‐old male patient who had an unusual presentation of an NK cell leukemia that was initially diagnosed as neuroblastoma. A bone marrow (BM) aspirate showed clumps of undifferentiated cells with the following phenotype: CD56bright+, CD33dim+, CD45‐, CD2‐, CD19‐, CD16‐, and CD57‐. Cytochemistry was noncontributory. The patient, having failed to respond to conventional neuroblastoma chemotherapy, was subsequently diagnosed as having NK cell leukemia based on functional in vitro assays. The patient responded to acute lymphoblastic leukemia (ALL) chemotherapy but relapsed 4 weeks into treatment and eventually died 25 weeks after initial presentation. The cell surface phenotype observed is consistent with a rare NK cell subset, the biology of which has not been well defined. Freshly isolated BM cells killed K562 cells in a conventional 51Cr‐release assay. Both interleukin‐2 (IL‐2) and interferon‐α (IFN‐α) induced LAK activity against the Daudi cell line. IL‐2 induced proliferation of the leukemic cells. TNF‐α, IFN‐γ, IL‐6, IL‐1ra, and TGF‐β levels were assessed and found to be concentrated in BM, in contrast to plasma samples. TNF‐α was present at a high concentration in BM (150.9 pg/ml), probably a reflection of the associated disease pathology of severe bone pain and pyrexia. In summary, this paper details clinical and laboratory investigations of a leukemia of a rare NK cell subset.