Uncommon cases of immature-type CD56+ natural killer (NK)-cell neoplasms, characterized by expression of myeloid antigen of blastic NK-cell lymphoma

Immature-type CD56⁺ natural killer (NK)-cell neoplasms are classified as either myeloid/NK-cell precursor acute leukemia or blastic NK-cell lymphoma. We identified two cases of immature-type CD56⁺ NK-cell neoplasms that were not categorizable as either of these entities. The first case involved a 74-year-old woman presenting with skin eruptions and pancytopenia due to bone marrow necrosis. Skin biopsy specimen revealed CD4⁺, CD7⁻, CD34⁻, CD43⁺, CD56⁺, CD68⁺, muramidase (lysozyme)⁺, and myeloperoxidase (MPO)⁻, and immunophenotyping of peripheral blood showed CD4⁺, CD7⁻, CD13⁺, CD33⁺, CD34⁻, CD43⁺, CD56⁺, cytoplasmic (cy)CD68⁺, CD123⁺, and HLA-DR⁺. The second case involved a 62-year-old man who had bilateral optic nerve tumor and presented with malignant cells in peripheral blood. Cell surface markers of malignant cells showed CD4⁺, CD7⁻, CD13⁺, CD33⁺, CD34⁻, CD43⁺, CD56⁺, cyCD68⁺, and HLA-DR⁺. The phenotypes of tumor cells in both cases were compatible with blastic NK-cell lymphoma, except for the expression of myeloid antigen. Clinical presentations of these cases showed characteristics of both blastic NK-cell lymphoma and myeloid/NK-cell precursor acute leukemia.