Key Points

  • Elevated yearlong leukocyte trajectories predicted PV disease evolution.

  • No yearlong hematologic lab value trajectories predicted thrombosis.

There are unresolved questions regarding the association between persistent leukocytosis and risk of thrombosis and disease evolution in polycythemia vera (PV), as much of the published literature on the topic does not appropriately utilize repeated measures data or time-dependent modeling to answer these questions. To address this knowledge gap, we analyzed a retrospective database of 520 PV patients seen at 10 academic institutions across the United States. Taking hematologic lab data at approximate 3-month intervals (or as available) for all patients for duration of follow-up, we used group-based trajectory modeling (GBTM) to identify latent clusters of patients who follow distinct trajectories with regards to their leukocyte, hematocrit, and platelet counts over time. We then tested the association between trajectory membership and hazard of two major outcomes: thrombosis and disease evolution to myelofibrosis, myelodysplastic syndrome, or acute myeloid leukemia. Controlling for relevant covariates, we found that persistently elevated leukocyte trajectories were not associated with hazard of thrombotic event (p = 0.4163), but were significantly associated with increased hazard of disease evolution in an ascending stepwise manner (overall p = 0.0002). Additionally, we found that neither hematocrit nor platelet count were significantly associated with hazard of thrombosis or disease evolution.

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