Why White Blood Cell Count Matters in Polycythemia Vera

Dr Lucia Masarova discusses leukocytosis as a clinically meaningful risk signal and management target in polycythemia vera and the importance of durable blood count control in reducing risk.

I would like to welcome you to this session. The title of this activity is “Why Blood Cell Count Matters in Polycythemia Vera.” My name is Lucia Masarova from MD Anderson Cancer Center, and it is a pleasure to be with you here today. As you'll know, maintaining hematocrit below 45% is the primary treatment goal in patients with polycythemia vera that was tied to control of the risk of hematocrit and thrombosis. However, polycythemia vera is not defined by hematocrit alone. It is polycythemia, so all the counts are affected and elevated. It's a chronic myeloproliferative neoplasm whose hallmark is to have polycythemia of all counts. Therefore, multiple blood count elevations are typical to be seen and indeed were discovered to play a role for disease behavior, especially regarding white cells. Patients may meet hematocrit targets but still have persistent leukocytosis, thrombocytosis, splenomegaly, or significantly uncontrolled symptoms, and all of those would contribute to the disease presentations and may be considered for intervention.

The broader clinical picture has become, therefore, significantly relevant for routine clinical practice. In this setting, despite achieving normally controlled hematocrit below 45%, one should pay attention to control of WBC spleen and symptoms. Particularly, white cell elevation as a key component of this broader assessment has been already shown to be associated with increased risk of thrombosis. We had the best results of the REVEAL study, which was a prospective observational study of more than 2000 patients with polycythemia vera, where elevated white cells over 12 billion per liter were associated with increased risk of thrombotic events and significant P value. The risk-adapted approach in these patients therefore is supporting prospective and in patients with low-risk PV otherwise, which means patients without thrombosis before and less than 60 years old who have controlled hematocrit below 45%. Persistent leukocytosis should be considered as one of the indications to initiate cytoreductive therapy.

Despite the hematocrit becoming the foundation or being the foundation of management of polycythemia vera, I would highlight to pay attention to the leukocytosis, which may indicate higher risk of thrombosis, especially in patients with intermediate or even low risk that would be uncontrolled. Management approach here should be to consider entire blood count profile, entire disease, including presentation of symptoms and splenomegaly, that would better align with the patient's treatment objectives and best clinical outcomes.

Thank you very much for listening. This was a talk on why blood cell count matters in patients with polycythemia vera. I would encourage you to complete a 1-question quiz now that you have completed my video.