Ruxolitinib is effective and safe in Japanese patients with hydroxyurea-resistant or hydroxyurea-intolerant polycythemia vera with splenomegaly.

Ruxolitinib, a potent JAK1/JAK2 inhibitor, was found to be superior to the best available therapy (BAT) in controlling hematocrit, reducing splenomegaly, and improving symptoms in the phase 3 RESPONSE study of patients with polycythemia vera with splenomegaly who experienced an inadequate response to or adverse effects from hydroxyurea. We report findings from a subgroup analysis of Japanese patients in RESPONSE (n = 18). The composite response rate (hematocrit control and spleen response) was higher in patients receiving ruxolitinib (50.0%) than in those receiving BAT (8.3%). A total of 50.0% of patients randomized to ruxolitinib achieved a spleen response vs 8.3% of those receiving BAT; 100 and 33.3% of patients in the respective groups achieved hematocrit control, with mean hematocrit in ruxolitinib-treated patients remaining stable at < 45% throughout the study. Similarly, a higher proportion of ruxolitinib-treated patients achieved complete hematologic remission (33.3 vs 16.7%). Ruxolitinib also led to rapid improvements in pruritus. All responses with ruxolitinib were durable to week 80, and its safety profile was consistent with that in the overall study. These findings suggest that ruxolitinib is an effective and well-tolerated treatment option for Japanese patients with polycythemia vera with an inadequate response to or adverse effects from hydroxyurea.