Malignant histiocytosis occurring with acute myelogenous leukemia in a patient with longstanding polycythemia vera.

A 52-year-old man with polycythemia vera of 20 years duration with progression to myelofibrosis developed a mass arising from the sternum. The mass consisted of large poorly differentiated cells infiltrating skeletal muscle, with cytochemical and ultrastructural features of malignant histiocytosis. At autopsy 6 weeks later, his bone marrow and spleen were involved by acute myelogenous leukemia. This is the first reported case of malignant histiocytosis occurring in a patient with polycythemia vera, and the second report of its association with acute myelogenous leukemia. There is suggestive evidence in this case that the malignant histiocytosis may possibly have arisen from the polycythemia vera clone.