Patients with myeloproliferative neoplasms (MPNs) have a higher rate of arterial and venous thrombosis than does the general population, with the greatest risk occurring around the time of diagnosis, according to results of a retrospective study.

Hazard ratios at 3 months after diagnosis were 3.0 (95% CI, 2.7-3.4) for arterial thrombosis and 9.7 (95% CI, 7.8-12.0) for venous thrombosis, compared with matched controls, Malin Hultcrantz, MD , PhD, of the Karolinska University Hospital, Stockholm, and her coauthors reported in the Annals of Internal Medicine .

Although previous studies have suggested patients with MPNs are at increased risk for thrombotic events, this large, population-based analysis is believed to be the first study to provide estimates of excess risk compared with matched control participants.

“These results are encouraging, and we believe that further refinement of risk scoring systems (such as by including time since MPN diagnosis and biomarkers); rethinking of recommendations for younger patients with MPNs; and emerging, more effective treatments will further improve outcomes for patients with MPNs,” the researchers wrote.

The retrospective, population-based cohort study included 9,429 Swedish patients diagnosed with MPNs between 1987 and 2009 and 35,820 matched control participants. Patient follow-up through 2010 was included in the analysis.

Thrombosis risk was highest near the time of diagnosis but decreased during the following year “likely because of effective thromboprophylactic and cytoreductive treatment of the MPN;”still, the risk remained elevated, the researchers wrote.

“This novel finding underlines the importance of initiating phlebotomy as well as thromboprophylactic and cytoreductive treatment, when indicated, as soon as the MPN is diagnosed,” they added.

Arterial thrombosis hazard ratios for MPN patients, compared with control participants, were 3.0 at 3 months after diagnosis, 2.0 at 1 year, and 1.5 at 5 years. Similarly, venous thrombosis hazard ratios were 9.7 at 3 months, 4.7 at 1 year, and 3.2 at 5 years.

Thrombosis risk was elevated in all age groups and all MPN subtypes, including primary myelofibrosis, polycythemia vera, and essential thrombocythemia. Of note, the study confirmed prior thrombosis and older age (60 years or older) as risk factors. Among patients with both of those risk factors, risk of thrombosis was increased 7-fold, according to the researchers.

Hazard ratios for thrombosis decreased during more recent time periods, suggesting a “positive effect” of improved treatment strategies, including increased use of aspirin as primary prophylaxis, better cardiovascular risk management, and better adherence to recommendations for cytoreductive treatment and phlebotomy, the researchers noted. Additionally, treatment with interferon and Janus kinase 2 inhibitors, such as ruxolitinib, “may be effective in further reducing risk for thrombosis,” the researchers wrote.

The study was funded by the Cancer Research Foundations of Radiumhemmet, the Swedish Research Council, and Memorial Sloan Kettering Cancer Center, among other sources. The researchers reported having no financial disclosures relevant to the study.

SOURCE: Hultcrantz M et al. Ann Intern Med. 2018. doi: 10.7326/M17-0028 .