Acute leukemia with the phenotype of a natural killer T cell bipotential precursor

An acute leukemia with an unusual immunophenotype developed in a 17-year-ol d girl. At the initial presentation, extramedullary involvement was not evi dent; but with advancing disease, massive splenomegaly and an osteolytic ri b tumor developed. The disease was aggressive and refractory to intensive c hemotherapeutic regimens for myeloid and lymphoid malignancies, and the pat ient died 3 months after the initial presentation. The leukemic cells were of irregular shape and variable size; they had deeply indented or bi-lobed nuclei and relatively fine, azurophilic granules in their cytoplasm. They w ere positive for acid phosphatase and beta-glucuronidase in granular staini ng, but they were negative for myeloperoxidase. The leukemic cells had a un ique immunophenotype: it was positive for T-cell antigens (CD1a, CD2, cytop lasmic CD3, CD4), myeloid antigens (CD13 and CD33), NK-cell antigen (CD56), CD19 and CD30. DNA analysis revealed no gene rearrangement in the T-cell r eceptor beta, gamma and delta, or immunoglobulin heavy chain genes. The leu kemic cells of our patient are thought to have arisen from the transformati on of a putative precursor cell common to both the T- and NK-cell lineage i n the bone marrow. The current literature on precursor NK-cell malignancy i s reviewed, and its clinicopathological feature is discussed.