Thrombosis in primary myelofibrosis: the influence of cohort composition and disease biology

This Swedish study evaluated 1079 patients with PMF or secondary MF compared with 5395 age- and sex-matched population controls. Overall, 40.7% of the patients had an International Prognostic Scoring System (IPSS) score of intermediate-2 or high risk. Rates of major bleeding, arterial events, and venous events were 2.55%, 2.59%, and 1.06% patient-years, respectively. Patients treated with JAK inhibitors (JAKi), mainly ruxolitinib and fedratinib, had higher event rates, including arterial and venous events (4.67% and 1.56% patient-years) and major bleeding (5.33% patient-years) than with interferon therapy (arterial 0.37% and venous 0.37% patient-years; bleeding 1.11% patient-years) or no therapy (arterial 2.15% and venous 0.79% patient-years; bleeding 2.32% patient-years). Lower hemoglobin (<11 g/dL) and higher white blood cells (>11 × 109/L) at diagnosis were associated with increased arterial event rates, particularly among patients who were treated with JAKi.