Transcript:Srdan Verstovsek, MD, PhD: Within polycythemia vera, we usually have two groups of patients. That is done based on assessment of risk of thrombosis. And the two factors that traditionally have been used to assess the risk of thrombosis are being age over 60 or history of blood clot. If any of these are present, in addition to standard phlebotomy to control hematocrit below 45% and aspirin to make blood flow easier, we do implement cytoreductive therapy to control the hematocrit below 45%, eliminate the phlebotomy need, and further decrease the risk of blood clotting. At this time, we also look at the white cells, platelets, spleen, and symptoms. So, cytoreductive therapy has wider use, not just to control the hematocrit and decrease thromboembolic events, but to control other factors that may contribute and control quality of life.

Hydroxyurea usually is the first-line therapy, sometimes interferon. Ruxolitinib has been developed now as a second-line therapy, a very effective therapy for all the five aspects of control of disease signs and symptoms. The disease is usually diagnosed in patients who are age 60 or older. The incidence is somewhere about 2.2 per 100,000 people, about 6000 to 7000 new cases in the United States. The average survival is about 20 years, so about 120,000, 140,000 people live with PV. I would say a majority are probably on cytoreductive therapy because they’re older than 60, but the real numbers are hard to actually define.

Daniel J. DeAngelo, MD, PhD: The risk of thrombosis is assessed in patients with polycythemia vera based on age, history of thrombotic event, and active coronary, cerebrovascular disease. It’s interesting that the height of the platelet count has not been shown to be a risk factor, although historically, we’ve used that as part of the risk models. But the height of the white count, the leukocyte count, has been shown to be a risk factor for thrombosis and development of cerebrovascular and cardiovascular disease. And so, these are the criteria that one needs to use for risk assessment—age, history of clotting, active coronary, cerebrovascular disease, and the height of the white cell count.

Srdan Verstovsek, MD, PhD: In polycythemia vera, we assess the risk of dying very rarely because people have a very good life expectancy. In polycythemia vera, the primary reason for assessment of any risk is the risk of thrombosis. Age and history of thrombosis have been traditionally used. We have knowledge from a number of papers in a retrospective nature that perhaps the presence of elevated white cell count at the beginning of therapy or developing white cell count during the course of the disease may contribute to the increased risk of thromboembolic events. Now, this is not yet used in everyday practice, but I think we are getting there because the number of papers and evidence is accumulating. Increased white cell count is part of the disease process and certainly contributes to the clotting formation. Controlling the white cell count in addition to controlling the red blood cell count is perhaps not just an indication for institution of the therapy, but is a valid goal of the therapy. On the other hand, let me just emphasize that the platelet number on its own is not a risk factor for thrombosis. Many times, patients are treated for a platelet number, which on its own, it’s not a risk factor for thrombosis.

Transcript Edited for Clarity