Thrombopoietin-responsive essential thrombocythaemia with myelofibrosis.

Platelet-derived growth factor (PDGF) and other cytokines released from megakaryocytes are thought to play a crucial role in the pathogenesis of myelofibrosis. We describe a patient with essential thrombocythaemia (ET) who developed myelofibrosis with an increased level of serum thrombopoietin (TPO). Recombinant human (rh) TPO stimulated the proliferation and spontaneous megakaryocyte colony formation of the neoplastic cells in the peripheral blood. Moreover, serum concentrations of PDGF, platelet factor 4, and beta-thromboglobulin were elevated and the production of these growth factors from the megakaryocyte progenitors was augmented with the addition of rhTPO in vitro. These results indicate that TPO may contribute to the development of myelofibrosis in ET.