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.

Background: Over the last decade, extracorporeal membrane oxygenation (ECMO) use in critically ill children has increased and is associated with favorable outcomes. Our study aims to evaluate the current status of pediatric ECMO in Korea, with a specific focus on its volume and changes in survival rates based on diagnostic indications. Methods: This multicenter study retrospectively analyzed the indications and outcomes of pediatric ECMO over 10 years in patients at 14 hospitals in Korea from January 2012 to December 2021. Four diagnostic categories (neonatal respiratory, pediatric respiratory, postcardiotomy, and cardiac-medical) and trends were compared between periods 1 (2012–2016) and 2 (2017–2021). Results: Overall, 1065 ECMO runs were performed on 1032 patients, with the annual number of cases remaining unchanged over the 10 years. ECMO was most frequently used for post-cardiotomy (42.4%), cardiac-medical (31.8%), pediatric respiratory (17.5%), and neonatal respiratory (8.2%) cases. A 3.7% increase and 6.1% decrease in pediatric respiratory and post-cardiotomy cases, respectively, were noted between periods 1 and 2.Among the four groups, the cardiac-medical group had the highest survival rate (51.2%), followed by the pediatric respiratory (46.4%), post-cardiotomy (36.5%), and neonatal respiratory (29.4%) groups. A consistent improvement was noted in patient survival over the 10 years, with a significant increase between the two periods from 38.2% to 47.1% (P = 0.004). Improvement in survival was evident in post-cardiotomy cases (30–45%, P = 0.002).Significant associations with mortality were observed in neonates, patients requiring dialysis, and those treated with extracorporeal cardiopulmonary resuscitation (P < 0.001). In pediatric respiratory ECMO, immunocompromised patients also showed a significant correlation with mortality (P < 0.001). Conclusion Pediatric ECMO demonstrated a steady increase in overall survival in Korea;however, further efforts are needed since the outcomes remain suboptimal compared with global outcomes.