Impact of age and time since diagnosis on thrombosis risk in myeloproliferative neoplasm patients: A nationwide register‐based matched cohort study

Thromboembolism is one of the major complications in myeloproliferative neoplasms (MPNs), especially in the initial years post-diagnosis and with increasing age. This nationwide matched cohort study used Swedish registers to assess whether attained age or time since diagnosis is more important for thrombosis risk. We identified 17 830 MPN patients diagnosed between 2001 and 2021, each matched with 10 population controls by sex, age and diagnosis year. Rates of first thrombosis post diagnosis and hazard ratios (HRs) were estimated using flexible parametric survival models over time since diagnosis and attained age. Thrombosis rates were significantly higher in MPN patients at all ages, especially in the first 2 years post-diagnosis, after which the rates remained higher than in age-matched controls. At 5 years, HR (95% confidence interval) for any thrombosis comparing patients to controls was 1.8 (1.7-1.9) at age 65, 1.6 (1.5-1.7) at age 70 and 1.5 (1.4-1.6) at age 75 and older. Attained age was more important than time since diagnosis, particularly in patients without prior thrombosis. Thrombosis rates were highest within the first 2 years post-diagnosis, then depended more on attained age than on time since diagnosis. These findings emphasize the importance of age and early management in MPN patients to optimize clinical care.