Essential Thrombocythemia in Young Individuals: Frequency and Risk Factors for Vascular Events and Evolution to Myelofibrosis in 126 Patients.

Vascular events and evolution to either myelofibrosis (MF) and acute leukemia (AL) are the main causes of morbidity and mortality in individuals with essential thrombocythemia (ET). However, the frequency of these complications in young ET patients is not well known. The objective of the present study was to assess the frequency of vascular events and the incidence of MF and AL in young patients with ET and to identify the factors associated with the development of such complications. In 126 subjects diagnosed with ET at a median age of 31 years (range: 5–40), overall survival and probability of survival free of either thrombosis, bleeding, MF, AL, and polycythemia vera (PV) were analyzed by the Kaplan-Meier method, followed by the log-rank test. With a median follow-up of eleven years (range: 4–25) three patients have died, being the probability of survival 98% at ten years. A total of 31 thrombotic events were registered in 25 patients; thrombosis-free survival (TFS) was 84% at ten years. Tobacco use was the only factor associated with an increased thrombotic risk, since TFS at 10 years was 72% in smokers versus 90% in non-smokers (p=0.03). Severe hemorrhagic complications were observed in 11 patients, and the estimated probability of bleeding-free survival was 92% at ten years. Evolution to MF was seen in 6 patients, four of whom had never received treatment for ET. MF-free survival was 97% at 10 years, with the risk being higher in patients showing an increased reticulin network in the bone marrow biopsy performed at diagnosis of ET (p=0.005). Transformation to AL was registered in one patient. JAK2 was mutated in 33 out of the 87 assessable patients (38%) and the mutation was associated with higher Hb values at diagnosis (p = 0.001). ET evolved into PV in five patients, being the probability of evolution into PV of 15% in JAK2 V617F positive patients versus 0% in JAK2 V617F negative patients (p=0.01). In conclusion, severe vascular complications are not infrequent in young subjects with ET, whereas transformation to MF or AL is a rare event.