Clinical characteristics in adolescents and young adults with polycythemia vera and essential thrombocythemia in Japan.

We report the first large-scale retrospective cohort study on adolescent and young adult (AYA) polycythemia vera (PV) and essential thrombocythemia (ET) in Japan, a subgroup analysis using Japanese multicenter registry data (JSH-MPN-R18). This study included patients with PV (n = 31) or ET (n = 141) aged 20 to 39 years at the initial visit. Hemorrhage-free survival (HFS) was better in AYA ET than in non-AYA ET (5-year HFS: 100% vs. 88.6%, p < 0.01), which might be attributed to differences in antithrombotic treatment rates between AYA and non-AYA patients. Although thrombosis-free survival did not differ statistically, the percentage of venous thrombotic events (TEs) among total TEs was higher in AYA compared to non-AYA PV and ET in Japan (26.0% vs. 6.0%, p < 0.01), but much lower than figures reported in European or US cohorts. Cytoreductive therapy (CRT) was administered to 25.8% of AYA patients with PV and 43.3% of AYA patients with ET, and the reason was usually unrelated to high risk of thrombosis. These results could be used to develop a more appropriate strategy for managing PV and ET in the Japanese AYA population.