Secondary myeloid/natural killer cell precursor acute leukemia following essential thrombocythemia.

The de novo leukemic transformation of essential thrombocythemia is a rare event, and usually associated with previous treatments. We describe a patient who received treatments with nitrosourea for long-standing essential thrombocythemia and subsequently developed extramedullary tumors, tentatively diagnosed as lymphoblastic lymphoma. Combination chemotherapy was initially successful, but relapsed with marked bone marrow involvement. Surface marker analysis revealed that the tumor cells had CD5, CD7, CD33, CD34, and CD56 antigens but lacked other T-cell, and B-cell markers. Immunogenotypical studies revealed germline configurations for both T-cell receptors and immunoglobulin genes. These clinical and phenotypical features are consistent with a myeloid/natural killer cell precursor leukemia, a recently proposed distinct clinical entity. To our knowledge, this is the first report of secondary leukemia of myeloid/ natural killer cell precursor origin, and suggest that myeloid/natural killer cell precursor might be a potent target of therapy-related leukemia.