• Malin Hultcrantz, Magnus Björkholm, Paul W Dickman, Ola Landgren, Åsa R Derolf, Sigurdur Y Kristinsson, and Andersson Therese M L TML Karolinska Institutet, Stockholm, Sweden (P.W.D., T.M.A.)..
• Karolinska University Hospital and Karolinska Institutet, Stockholm, Sweden, and Memorial Sloan Kettering Cancer Center, New York, New York (M.H.).
• Ann. Intern. Med. 2018 Mar 6; 168 (5): 317-325.

BackgroundPatients with myeloproliferative neoplasms (MPNs) are reported to be at increased risk for thrombotic events. However, no population-based study has estimated this excess risk compared with matched control participants.ObjectiveTo assess risk for arterial and venous thrombosis in patients with MPNs compared with matched control participants.DesignMatched cohort study.SettingPopulation-based setting in Sweden from 1987 to 2009, with follow-up to 2010.Patients9429 patients with MPNs and 35 820 matched control participants.MeasurementsThe primary outcomes were rates of arterial and venous thrombosis. Flexible parametric models were used to calculate hazard ratios (HRs) and cumulative incidence with 95% CIs.ResultsThe HRs for arterial thrombosis among patients with MPNs compared with control participants at 3 months, 1 year, and 5 years were 3.0 (95% CI, 2.7 to 3.4), 2.0 (CI, 1.8 to 2.2), and 1.5 (CI, 1.4 to 1.6), respectively. The corresponding HRs for venous thrombosis were 9.7 (CI, 7.8 to 12.0), 4.7 (CI, 4.0 to 5.4), and 3.2 (CI, 2.9 to 3.6). The rate was significantly elevated across all age groups and was similar among MPN subtypes. The 5-year cumulative incidence of thrombosis in patients with MPNs showed an initial rapid increase followed by gentler increases during follow-up. The HR for venous thrombosis decreased during more recent calendar periods.LimitationNo information on individual laboratory results or treatment.ConclusionPatients with MPNs across all age groups have a significantly increased rate of arterial and venous thrombosis compared with matched control participants, with the highest rates at and shortly after diagnosis. Decreases in the rate of venous thrombosis over time likely reflect advances in clinical management.Primary Funding SourceThe Cancer Research Foundations of Radiumhemmet, Blodcancerfonden, the Swedish Research Council, the regional agreement on medical training and clinical research between Stockholm County Council and Karolinska Institutet, the Adolf H. Lundin Charitable Foundation, and Memorial Sloan Kettering Cancer Center.

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