Risk factors for vascular complications in
polycythemia vera (PV) include laboratory and clinical findings. Among laboratory values, the hematocrit has been clearly associated with
thrombosis, particularly in the cerebral circulation. Platelet count is a possible but not yet clearly established predictor of vascular complications. Platelet function tests are of little help in prognostic evaluation because most attempts to correlate these abnormalities with clinical events have been disappointing. Clinical predictors of
thrombosis include increasing age and a previous history of vascular events. Identifying risk factors for
thrombosis is important to initiate
therapy. Phlebotomy is associated with an increased incidence of
thrombosis in the first 3 to 5 years, whereas
chemotherapy may induce a higher risk of secondary
malignancies after 7 to 10 years of follow-up. New cytoreductive drugs virtually devoid of mutagenic risk include
interferon-alpha and
anagrelide, but their role in reducing thrombotic complications remains to be demonstrated. Antithrombotic drugs, such as
aspirin, are frequently used in PV, despite doubts regarding safety and efficacy. Two recent studies from the Gruppo Italiano Studio Policitemia Vera (GISP) assessed the rate of major
thrombosis as well as the tolerability of low-dose
aspirin in PV patients. These investigations created a favorable scenario for launching a European collaborative clinical trial (ECLAP study) aimed at testing the efficacy of low-dose
aspirin in preventing
thrombosis and prolonging survival in patients with PV.