Thrombosis in myelofibrosis: prior thrombosis is the only predictive factor and most venous events are provoked.

In a retrospective analysis of 205 patients (median age 62 years) with primary myelofibrosis and known JAK2V617F mutational status, 13.2% experienced a vaso-occlusive event at or prior to their diagnosis. After a median follow up of 31 months, post-diagnosis thrombosis occurred in 22 patients (10.7%), including 9 (4.4%) and 16 (7.8%) patients with a total of 9 arterial and 24 venous events, respectively. The majority (71%) of the venous events were temporally associated with other exogenous risk factors for thrombosis such as surgery, line placement or hormonal therapy. On multivariable analysis that included age, JAK2V617F mutation status and leukocyte count as covariates, history of thrombosis was the only predictive variable in general (P=0.04) or when arterial (P=0.007) and venous (P=0.02) thromboses were analyzed separately. The current study demonstrates a higher prevalence of venous, as opposed to arterial, events in PMF, post-diagnosis, and clarifies their nature as being mostly provoked.