Chronic myelomonocytic leukemia transformation in polycythemia vera.

Myelodysplasia is an increasingly recognized complication of polycythemia vera (PCV) which often precedes leukemic transformation. This paper describes two patients with aggressive chronic myelomonocytic leukemia, previously undescribed as a complication of PCV. Both patients presented with rapidly increasing splenomegaly which was resistant to treatment with hydroxyurea and external beam irradiation. Splenectomy precipitated fatal hepatic failure in one patient. The other died shortly after transformation to acute myelomonocytic leukemia (FAB M4 classification). Pathology of the bone marrow, spleen, and liver was remarkable for extensive infiltration by dysplastic myeloid elements. Survival was short, only 4-6 months from diagnosis. The unique characteristics in these patients were: (i) prior history of PCV; (ii) rapidly increasing splenomegaly resistant to standard therapy; (iii) absence of overt marrow fibrosis; (iv) hypercellularity (greater than or equal to 90% cellular) of the bone marrow with dysplasia in the myeloid, erythroid, and megakaryocytic cell lines; (v) peripheral monocytosis greater than 1 x 10(9); and (vi) extensive infiltration of the spleen and liver by dysplastic myeloid cells. In addition, the patient who subsequently developed acute leukemia had been treated with hydroxyurea under the PVSG-08 protocol, providing further evidence of the potential leukemogenic effects of this agent.