“Management of acute thrombosis and long-term management of venous thrombosis at usual sites in patients with MPNs should be the same as [management of] DVT or PE occurring in [patients without MPNs], except that the role of DOACs in these patients, especially those with high risk, has not been established,” the authors stated.

Following first VTE at these sites, clinicians should attempt to balance the risks for hemorrhagic complications and recurrent VTE when determining secondary VKA prophylaxis duration. Although the authors recommended long-term treatment with VKAs for these patients, they acknowledged that DOAC usage may also be considered on an individual basis, as DOACs have demonstrated efficacy in small numbers of patients.

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Treating Thrombosis at Unusual Sites

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Splanchnic vein thrombosis is “one of the main features of MPNs” with a prevalence ranging from 1% to 23% in patients with MPNs and requires a multidisciplinary treatment approach. Once again, anticoagulation with LMWH combined with VKA treatment is considered the standard of care. However, patients may also require antiplatelet and cytoreductive treatment, placement of stents in the abdominal veins, thrombolysis, or liver transplant. Usage of DOACs is currently not recommended.

Patients with MPNs who are pregnant experience physiological changes in their hemostatic pathways that put them at increased risk for thrombosis. Unless contraindicated, pregnant patients should receive aspirin throughout their pregnancy and should be followed in joint obstetric and hematology clinics. For patients deemed high-risk, prophylactic doses of LMWH are recommended during pregnancy and at 6 weeks postpartum.

Clinical Perspectives on Treating Thrombosis

Josef Prchal, MD, of the University of Utah and Huntsman Cancer Center in Salt Lake City, Utah, told Hematology Advisor more research is needed to determine how best to prevent DVT and PE in this patient population. “Some people believe that if you achieve normalization of blood counts, then your risk for thrombosis is equal to [the risk of thrombosis in] controls, [meaning people] who do not have polycythemia vera or essential thrombocythemia. That needs to be investigated,” Dr Prchal said.

Prithviraj Bose, MD, of MD Anderson Cancer Center in Houston, Texas, noted that overall, this review does a good job of reviewing the pathophysiology and risk factors for thrombosis and the management of thrombosis in patients with MPNs. “There are some contentious statements, however, that touch on areas where opinions may vary. For example, we believe that the goal of cytoreductive therapy in polycythemia vera should be to eliminate phlebotomy, not just reduce its frequency. There are data from Spain, for instance, that show that those who require 3 or more phlebotomies a year while on hydroxyurea have more thrombotic events,” Dr Bose told Hematology Advisor.

He added that experts currently have differing opinions on whether patients with polycythemia vera and JAK2-mutated essential thrombocythemia who have splanchnic vein thrombosis should receive aspirin treatment in addition to anticoagulation and cytoreductive therapy. “Personally, I do use DOACs in patients with MPNs and thrombosis and don’t see a reason not to. Although it is true that this has not been extensively studied, there are emerging data for their safety and efficacy in patients with MPNs,” said Dr Bose. Furthermore, he pointed out that all 3 commonly used DOACs now have reversal agents available, and there are now published data on their safety and efficacy in patients with cancer in general.

Adan Rios, MD, of McGovern Medical School at The University of Texas Health Science Center in Houston, agreed that this review article was well researched but added it could have benefited from a discussion indicating the risk for thrombosis associated with mutations. “The risk for thrombosis is not equal among all MPNs, and it depends on the mutations [the patient] expresses,” Dr Rios told Hematology Advisor. “[The review authors] are correct in stating that the use of DOACs in patients with MPNs and thrombosis needs further study.”

He added that randomized studies to assess patients receiving VKAs, LMWH injections, and DOACs based on their risk factors are needed. According to Dr Rios, factors such as age and poor international normalized ratio control can play a role in what anticoagulant to use. “For example, DOACs are associated with a lower rate of bleeding,” he explained, “and thus the potential benefit in patients at risk for novel bleeding during VKA therapy is in need of investigation. A randomized study taking into account clinical variables can provide the answer to these questions. VKA therapy is not easy to use, but until now, in the absence of these studies, it [has been] the most commonly used, despite its significant drawbacks.”


1.     Arachchillage DRJ, Laffan M. Pathogenesis and management of thrombotic disease in myeloproliferative neoplasms [published online August 5, 2019]. Semin Thromb Hemost. doi:10.1055/s-0039-1693477