Alpha-interferon in polycythemia vera and essential thrombocythemia.

Twenty-one patients with chronic myeloproliferative disorders, eleven with polycythemia vera (PV) and ten with essential thrombocythemia (ET), were treated with small doses of alpha-2a interferon (IFN). The median follow-up was, respectively, 10.8 months (range 4-22) for PV and 8.11 months (range 4-16) for ET. Six patients with PV and five with ET had been previously treated with conventional cytotoxic drugs, while the remaining patients were newly diagnosed. In four patients with PV we observed a durable normal hematocrit level (PCV less than 0.48) and a reduction of platelet count and spleen size within 4-8 weeks of treatment. Three patients achieved moderate disease control. In the others the disease remained substantially unchanged. Five out of nine evaluable patients with ET showed complete response (CR) within six weeks, one patient had a partial response (PR) and three no response (NR). In one patient with ET the IFN therapy was stopped after twelve days because neurological side effects were observed. All the other patients tolerated long-term treatment very well.