Natural killer cell precursor acute lymphoma/leukemia presenting in an infant.

Lymphoma/leukemia derived from immature natural killer (NK) cells occur most commonly in adults and are characterized by blastic cytologic features and an aggressive outcome. Predilection for extranodal sites and absence of the Epstein-Barr virus associated with mature NK cell malignancies further distinguish this entity. We present a NK precursor acute lymphoma presenting with multiple masses in an infant without circulating blasts or marrow replacement by disease. The diagnostic difficulty arose from several factors, including young age, presentation with multiple masses, blastic cytologic features mistaken for a small, round, blue cell tumor, and the absence of lineage-specific markers. The CD56+, CD34+, CD33+, MPO-, cytoplasmic CD3+, CD45-, CD7-, HLA-DR-, and TdT- immunophenotype of this neoplasm overlaps with previously reported cases of myeloid/NK precursor acute leukemia and blastic NK cell lymphoma/leukemia. This case emphasizes the need for a strong index of suspicion to recognize this rare entity and to distinguish it from solid tumors and other hematolymphoid neoplasms that occur in infancy.