REVEAL: Elevated WBC count and thrombotic events in PV

Between 34% and 41% of patients with polycythemia vera (PV) experience thrombotic events (TE). Established risk factors for TE include JAK2 mutation, advanced age, TE history, and elevated hematocrit.¹ In addition, retrospective studies have shown elevated white blood cell (WBC) count to be associated with increased TE risk.¹ Here, we summarize a prospective, observational study by Gerds et al.¹ published in Blood which investigated association between WBC count and TE in patients with PV enrolled in the REVEAL study.¹

REVEAL study design

• REVEAL (NCT02252159) investigated patients ≥18 years with PV with a history of, or a plan to undergo, allogeneic stem cell transplant (allo-HCT) within 3 months of enrollment.
• Data were collected for 6 months across centers in the US, from July 2014 to August 2016.
  • Median follow-up was 44.7 months.
• A covariate Cox proportional hazards model was used to assess the association between WBC count and TE occurrence.

Key findings

• Overall, 2,271 patients with PV were included.
  • Median age was 67 years, and 54.1% of patients were male.
  • More patients were classed as high risk than low risk (77.9% vs 22.1%).
  • Median disease duration from diagnosis was 4.1 years, and 20.1% of patients had a history of TE.
• Within the population analyzed, 4.7% experienced TEs at an incidence of 1.36/100 patient-years, and most experienced one event compared with two to five events (81.1% vs 18.9%, respectively).
  • The cumulative incidence of venous TEs was higher than arterial TEs (3.13% vs 1.54%).
  • The cumulative incidence of TEs occurring in patients classed as high risk was higher than patients classed as low risk (5.2% vs 2.78%).
• TE occurrence was significantly associated with elevated blood counts (Table 1).

HCT, hematocrit level; HR, hazard ratio; NEUT, absolute neutrophil count; NS, not significant; PLT, platelet; TE, thrombotic event; WBC, white blood cell count.

*Adapted from Gerds, et al.¹

^†Association significance was not sustained a year after initial assessment.

• When comparing high-risk vs low-risk, WBC was associated with increased risk of TE in both subgroups and was the only association found in patients with low risk.
  • In high-risk patients, male sex, HCT, and PLT were also associated with increased risk of TE.

Key learnings

Age, TE history, and elevated hematocrit were confirmed as risk factors of increased TE incidence in patients with PV from this observational study. Elevated WBC count was found to be significantly associated with TE occurrence in PV in both high- and low-risk patients. This study supports the addition of WBC into PV risk stratification. This addition could aid in the development of future treatment options to better manage PV and the associated TE risk.