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I am happy to present these results on behalf of the Yale Cancer Outcomes Public Policy and Effectiveness Research Center investigators. I will be talking about the impact of phlebotomy and hydroxyurea on survival and risk of thrombosis among all the patients with polycythemia vera.
Polycythemia vera is a classical myeloproliferative neoplasm characterized by the overproduction of immature red blood cells and increased incidents of thrombotic events. The major goal of therapy is to prevent thrombosis. High risk PV patients are defined as patients who are older than 60 or had prior history of thrombosis. Phlebotomy is indicated for all patients with polycythemia vera, including high and low risk patients, and the goal for phlebotomy is hematocrit less than 45%. Cytoreductive treatment is reserved for high risk patients only, and hydroxyurea is recommended as the frontline therapy for European, as well as United States guidelines.
The goal of our study was to evaluate use of phlebotomy and hydroxyurea and their impact on overall survival and incidents of thrombosis among all the patients with polycythemia vera in real world setting. We used SEER-Medicare Linked Database to study PV patients who were diagnosed between 2007 and 2013. Age of our patients was between 66 and 99 years old at the time of diagnosis. They were to have continuous Medicare Part A, Part B, and Part D coverage during the study period, and we excluded patients who were members of HMO because their claims data was not available for our analysis. The end of follow-up was December 2014 or death.
We looked at two treatments, phlebotomy and hydroxyurea, and assessed the influence on overall survival, as well as thrombotic events after diagnosis. We used Kaplan-Meier curves and log-rank tests to assess an adjusted overall survival and incidence rates of thrombotic events. Multivariate Cox proportional hazard regression model was used to estimate the adjusted effect of treatments on overall survival rates and thrombotic events.
We identified 832 polycythemia vera patients meeting eligibility criteria. Among those patients, 18% were treated with hydroxyurea only, 35% received both treatments, and this can be considered adequate based on current guidelines. 19% received neither hydroxyurea nor phlebotomy and 28% received phlebotomy only. Those 47% of our patients were undertreated based on current guidelines.
We also looked at additional cytoreductive treatments received by identified PVR patients and found that very few used interferon or busulfan and about 2% used ruxolitinib which is approved as a second line treatment for PVR patients, as well as for patients with myelofibrosis.
In the multivariate Cox model, which compared patients who received treatment to patients who didn't receive phlebotomy or hydroxyurea, we show that phlebotomy only, hydroxyurea only, and especially both treatments are associated with improved survival. Similarly, when treatments were assessed in regards to their influence on thrombotic events, phlebotomy only, hydroxyurea only, and both treatments when compared to no treatment were associated with improved outcomes, specifically, less thrombotic events.
Based on our results, we conclude that the use of phlebotomy and hydroxyurea is associated with improved overall survival, decreased incidents of thrombosis, as well as both treatments, and are used in high risk polycythemia vera patients. NCCN MPN guidelines adopted in September of 2017 are timely, and implementation of those guidelines is needed to improve patients' outcomes.