Differences in Clinical Outcomes Between Hydroxyurea-Resistant and-Intolerant Polycythemia Vera Patients

Background: Previous studies have suggested that patients with polycythemia vera (PV) who exhibit hydroxyurea-resistance (HU-R) and-intolerance (HU-I) may have distinct characteristics and clinical outcomes. However, to date, no studies have reported a comparison between these two groups or assessed prognostic factors in these patients. Methods: The objective of this study was to evaluate clinical outcomes and identify prognostic factors among PV patients with HU-R or HU-I. We conducted a review of PV patients who received frontline treatment with HU from nine centers and identified 90 patients with HU-R or HU-I. Results: The cumulative incidence of thrombosis after 7 years of HU-R/I was 21.4%, and the incidence of disease progression was 22.5%. Comparing the HU-R and HU-I groups, the HU-R group had a significantly higher rate of disease progression (36.7% vs. 0.56%, P = 0.009), while there was no significant difference in thrombosis incidence (19.0% vs. 22.9%, P = 0.463). Multivariate analysis revealed that HU-R was an independent prognostic factor for progression-free survival (hazard ratio, 6.27, 95% confidence interval, 1.83-21.47, P = 0.003). Additionally, higher lactate dehydrogenase levels, multiple cardiovascular risk factors, and prior thrombosis were identified as unfavorable predictors of overall survival. Conclusion: These findings suggest that patients with HU-R face a higher risk of hematological transformation, but have a comparable risk of thrombosis to patients with HU intolerance. These distinctions should guide decisions on second-line treatment options and clinical trials involving these patients.