SAN ANTONIO—Patients with polycythemia vera face an elevated risk of thromboembolic events and cardiovascular disease, compared to patients with other myeloproliferative disorders.
A German-led study last year in Annals of Hematology pointed out that CV conditions are the major cause of morbidity and mortality in PV patients, adding that vascular complications such as arterial or venous thrombosis often leads to the diagnosis of PV.1
Now, a veteran study has underscored the risk PV patients have of thrombotic events. An analysis in Clinical Lymphoma, Myeloma & Leukemia sought to describe the association between white blood cell levels and occurrence of TEs among patients with PV from a large real-world population.2
The study team, which involved researchers from the University of Texas Health San Antonio and the MD Anderson Cancer Center, conducted a retrospective analysis using VHA claims data from Oct. 1,2005, to Sept. 30, 2012, to evaluate adult patients assigned to four WBC count categories:
- < 7.0,
- 0-8.4,
- 5 to < 11.0, and
- ≥ 11.0 × 109/L)
Of the 1565 patients with PV included in the analysis, the WBC count was < 7.0 × 109/L for 428 (27.3%), 7.0 to 8.4 × 109/L for 375 (24.0%), 8.5 to < 11.0 × 109/L for 284 (18.1%), and ≥ 11.0 × 109/L for 478 (30.5%). The study noted that 390 (24.9%) had experienced a TE during the study period.
Over a mean follow-up period ranging from 3.6 to 4.5 years, the hazard ratio for TEs was determined to be 1.10 (95% confidence interval [CI], 0.82-1.48; P = .5395), 1.47 (95% CI, 1.10-1.96; P = .0097), and 1.87 (95% CI, 1.44-2.43; P < .0001) for patients with a WBC count of 7.0 to 8.4, 8.5 to < 11.0, and ≥ 11.0 ×109/L, respectively, compared with the reference group with WBC count < 7.0 ×109/L)..
“A positive, significant association between an increased WBC count of ≥ 8.5 ×109/L and the occurrence of TEs was observed in patients with PV,” the authors concluded. “The potential thrombogenic role of WBCs in patients with PV supports the continued inclusion of WBC count control in disease management and evaluation of the response to therapy.”
The Annals of Hematology study explained that the highest rates of thrombosis typically occur shortly before or at diagnosis and decrease over time, probably due to the effects of treatment.
That review pointed out that important risk factors include age of 60 and older and a history of thrombosis. Elevated hematocrit and leukocytosis also are associated with an increased risk of thrombosis, the authors said.
“Low-risk patients (< 60 years old with no history of thrombosis) are managed with phlebotomy and low-dose aspirin, whereas high-risk patients (≥ 60 years old and/or with a history of thrombosis) should be treated with cytoreductive agents,” those researchers wrote. “Interferon and ruxolitinib are considered second-line therapies for patients who are intolerant of or have an inadequate response to hydroxyurea, which is typically used as first-line therapy.”
- Griesshammer M, Kiladjian JJ, Besses C. Thromboembolic events in polycythemia vera. Ann Hematol. 2019 May;98(5):1071-1082. doi: 10.1007/s00277-019-03625-x. Epub 2019 Mar 8. PubMed PMID: 30848334; PubMed Central PMCID: PMC6469649.
- Parasuraman S, Yu J, Paranagama D, et al. Elevated White Blood Cell Levels and Thrombotic Events in Patients With Polycythemia Vera: A Real-World Analysis of Veterans Health Administration Data. Clin Lymphoma Myeloma Leuk. 2020;20(2):63–69. doi:10.1016/j.clml.2019.11.010
I can understand the good intentions of the conclusions. But before issuing such strong statements on what we “should” do, wouldn’t randomized trials be indicated rather than relying on associations? It seems we have, as a profession, made this mistake before.