A hybrid form of myeloid/NK-cell acute leukemia and myeloid/NK-cell precursor acute leukemia.

Natural killer (NK)-cell leukemia/lymphoma is a rare entity that has been defined only in recent years. In the Revised European-American Lymphoma and World Health Organization classifications, only the mature NK-cell malignancies are included. However, at least 3 types of precursor NK-cell neoplasms have been reported in the literature. These include myeloid/NK-cell acute leukemia, myeloid/NK-cell precursor acute leukemia, and blastic NK-cell lymphoma/leukemia. These leukemias are characterized by the presence of blasts, which express CD56, in the peripheral blood, bone marrow, lymph nodes, and/or extranodal tissues. We report a case that is morphologically consistent with myeloid/NK-cell acute leukemia but immunologically is myeloid/NK-cell precursor acute leukemia. This case is unique in its cutaneous presentation without involvement of the peripheral blood. Extensive flow cytometric studies were performed on the skin biopsy and bone marrow aspirate specimens, which included many markers that had not been tested before in these entities. The clinical implications of these findings are discussed.