CD7(-KILLER-CELL PRECURSOR ACUTE-LEUKEMIA - A DISTINCT HEMATOLYMPHOIDDISEASE ENTITY() AND CD56(+) MYELOID NATURAL)

The disease spectrum of natural killer (NK) cell leukemias and lymphom as has recently been expanding with the continuing evolution in diagno stic concepts. We describe here seven cases of acute leukemia of conce ivable myeloid and NK cell precursor phenotype in six men and one woma n varying from 19 to 59 years of age (median, 46 years). Striking extr amedullary involvement was evident at initial presentation, with perip heral lymphadenopathy and/or mediastinal masses. Two lacked any leukem ic cells in the bone marrow at diagnosis. Using cytochemical myelopero xidase staining, less than 346 of the leukemic cells showed positive r eactivity. However, expression of CD7, CD33, CD34, CD56, and frequentl y HLA-Dp, but not other NK, T-cell, and B-cell markers was observed. C ytoplasmic CD3 was detected in three of the cases by flow cytometry an d in six by Northern blotting, suggesting an origin from common progen itors between the NK cell and myeloid lineages. All but one presented germline configurations of the T-cell receptor beta and gamma chain ge nes and Ig heavy chain gene. With regard to morphology, the cells were generally L2-shaped, with variation in cell size, round to moderately irregular nuclei and prominent nucleoli, pale cytoplasm, and a lack o f azurophilic granules. Histopathologic examination of biopsied specim ens of extramedullary tumors showed a lymphoblast-like morphology, imp lying the differential diagnostic problem from lymphoblastic lymphomas , especially in cases lacking bone marrow involvement. Three patients were successfully treated with chemotherapy for acute myeloid leukemia (AML), whereas three other patients proved refractory to chemotherape utic regimens for lymphoid malignancies, although two responded to sub sequent AML chemotherapy. However, despite intensive chemotherapy, inc luding allogeneic bone marrow transplantation, most persued fatal cour ses within 41 months. These data suggested that the CD7(+) and CD56(+) myeloid/NK cell precursor acute leukemia might constitute a distinct biologic and clinical disease entity. Its recognition appears to be pa rticularly important for the clinicopathologic evaluation of CD56(+) h ematolymphoid malignancies and the development of therapeutic approach es to such disease. (C) 1997 by The American Society of Hematology.