Prognostic factors for thrombosis-free survival and overall survival in polycythemia vera: A retrospective analysis of 623 PTS With long follow-up

JAK2 V617F as a Marker for Long-Term Disease Progression and Mortality in Polycythemia Vera and its Role in Economic Modeling

BACKGROUND

In order to facilitate sound economic evaluations of novel treatments, health-economic models of polycythemia vera (PV) must combine effects on surrogate endpoints in trials with disease progression (DP) and mortality in long-term cohort data.

OBJECTIVE

We validate an economic model for PV that uses Janus Kinase 2 (JAK2) burden as a surrogate endpoint to predict DP (thrombosis, myelofibrosis, and acute leukemia) and overall survival (OS) based on progression-specific mortality.

METHODS

Long-term observational studies that include information about baseline JAK2 burden were identified via PubMed searches and used to validate the model. Kaplan-Meier (KM) OS curves were extracted using a digitizing software. External validity of the model was analyzed by visually comparing OS curves of the model with the KM curves of the included studies, as well as calculating differences in mean OS estimated as area under the curve (AUC).

RESULTS

The model's predictions of cumulative DP were somewhat lower than the published studies. Over 20 years' time, our base case model predicted a mean OS for a PV patient (15.0-16.5 years), which was in line with the published studies (15.8-17.5 years). Modeled mean OS was almost two years longer (1.6-1.9 years) for patients with JAK2 <50% than patients with JAK2 ≥50%. Only three long-term observational studies that satisfied the predefined criteria were found and could be used in the validation, but these studies did not capture JAK2 evolution over time. Improved model predictions of DP and mortality based on the longitudinal evolution of JAK2 could be derived from real-world data sources. Such data are currently scarce and future observational studies should be designed to capture the long-term impact of JAK2 on DP and mortality in PV.

CONCLUSIONS

Our model, based on JAK2 burden as a marker for DP, generated OS estimations that are in line with results of published data.

How I treat polycythemia vera

Since its discovery, polycythemia vera (PV) has challenged clinicians responsible for its diagnosis and management and scientists investigating its pathogenesis. As a clonal hematopoietic stem cell (HSC) disorder, PV is a neoplasm but its driver mutations result in overproduction of morphologically and functionally normal blood cells. PV arises in an HSC but it can present initially as isolated erythrocytosis, leukocytosis, thrombocytosis, or any combination of these together with splenomegaly or myelofibrosis, and it can take years for a true panmyelopathy to appear. PV shares the same JAK2 mutation as essential thrombocytosis and primary myelofibrosis, but erythrocytosis only occurs in PV. However, unlike secondary causes of erythrocytosis, in PV, the plasma volume is frequently expanded, masking the erythrocytosis and making diagnosis difficult if this essential fact is ignored. PV is not a monolithic disorder: female patients deregulate fewer genes and clinically behave differently than their male counterparts, while some PV patients are genetically predisposed to an aggressive clinical course. Nevertheless, based on what we have learned over the past century, most PV patients can lead long and productive lives. In this review, using clinical examples, I describe how I diagnose and manage PV in an evidence-based manner without relying on chemotherapy.