Polycythemia vera in young patients: a study on the long-term risk of thrombosis, myelofibrosis and leukemia.

BACKGROUND AND OBJECTIVES Polycythemia vera (PV) is unusual in young patients, so that little information is available on long-term clinical evolution in this particular group. The aim of this study was to define the long-term risk of thrombosis, acute leukemia (AL) and myelofibrosis with myeloid metaplasia (MMM) in young PV patients. DESIGN AND METHODS From 1975 to 2000, 70 PV patients aged less than 50 years were followed for a median time of 14 years (range 2-26). About three quarters were treated with pipobroman. The Kaplan-Meier method and Cox regression were used for survival analysis. The standardized mortality ratio (SMR) was calculated using Italian age/sex specific mortality rates. RESULTS The risk of thrombosis increased during the observation period, reaching a plateau of 14% at 10 years and was markedly higher in individuals with a previous history of thrombosis (p=0.0023). No patient had progression into AL or MMM before the 9th year of follow-up. Subsequently, five patients (7%) developed AL and five (7%) MMM, with a 20-year cumulative risk of 15% and 10%, respectively. Overall survival at 20 years was 62%, with nine patients dying of progression into AL or MMM, four of vascular events, one of lung cancer, and four of non-PV-related causes. The SMR was 5.3, indicating a mortality significantly higher than that of the general population (p<0.000). INTERPRETATION AND CONCLUSIONS This long-term retrospective cohort study shows that although the median survival of young patients with PV exceeds 23 years, their life expectancy is markedly lower than that of the general population because of disease evolution into AL or MMM.