Hematocrit control and thrombotic risk in patients with polycythemia vera treated with ruxolitinib in clinical practice

Abstract Polycythemia vera (PV) is a myeloproliferative neoplasm characterized by unregulated red blood cell production resulting in elevated hemoglobin (HGB) and/or hematocrit (HCT). Patients often have clinical symptoms such as fatigue, pruritus, and painful splenomegaly but are also at increased risk of thrombosis, both venous and arterial. Ruxolitinib, a selective JAK inhibitor, is approved by the US Food and Drug Administration as second-line cytoreductive treatment after intolerance or inadequate response to hydroxyurea. Though ruxolitinib has been widely used in this setting, limited data exist in the literature on ruxolitinib treatment patterns and outcomes among patients with PV in routine clinical practice. We report a retrospective, observational, cohort study of patients treated for PV with ruxolitinib across three US centers (academic and regional practice) from December 2014-December 2019. We identified 69 patients with a median follow-up was 3.7 years (95% CI, 2.9 to 4.4). Our data demonstrate very high rates of HCT control (88% of patients by three months and 89% by six months); few patients required dose adjustments or suspension during the study period. No arterial thromboses were observed and we found that one patient had a thrombotic event in the setting of a second malignancy. We also found that 28% of patients initiated ruxolitinib as a result of poorly controlled platelet counts, second only to hydroxyurea intolerance (46%). In clinical practice, ruxolitinib continues to be effective in controlling HCT after three and six months of treatment in patients with low thrombotic risk.