The RESPONSE-2 trial showed that ruxolitinib was effective and well-tolerated for long-term treatment, making it a good choice for second-line therapy in patients with inadequately controlled polycythemia vera (PV) without splenomegaly.
RESPONSE-2 was a phase IIIb study that randomized 149 patients with PV without splenomegaly who were intolerant of or resistant to hydroxyurea to receive ruxolitinib or best available therapy for up to 80 weeks. At the time of patient randomization best available therapy regimens included hydroxyurea (n=38), interferon or pegylated interferon (n=9), pipobroman (n=5), lenalidomide (n=1), or no treatment (n=22). Median follow-up was 67 months.
“The primary analysis of the RESPONSE-2 study showed superiority of ruxolitinib versus best available therapy for hematocrit control, normalizing blood cell counts, and improving PV symptoms at week 28,” study researchers wrote. “This results of this five-year analysis of the RESPONSE-2 study confirm and extend these findings.”
Between study weeks 28 and 80, the majority (77%) of patients assigned to best available therapy crossed over to ruxolitinib. None continued best available therapy after week 80.
Ninety-seven patients continued on ruxolitinib until week 260. This included 80% of patients assigned to the drug and 66% of patients who crossed over.
At week 260, 22% of patients assigned to ruxolitinib had durable hematocrit control with estimated median duration not reached. This could not be estimated in the best available therapy group because of the small number of patients remaining in this arm.
During the five-year follow-up period, median hematocrit level among patients assigned to ruxolitinib remained below 45%. At week 260, 12% of patients assigned ruxolitinib achieved durable complete hematological remission. The median duration of complete remission was 34 weeks.
Five-year overall survival was 96% in the ruxolitinib group and 91% in the best available therapy group.
“Ruxolitinib provided a substantial benefit in the crossover group versus the best available therapy group; however, the benefit was larger in patients treated with ruxolitinib (ie, those initiating ruxolitinib after the first sign of hydroxyurea failure) than in crossover patients (ie, those with a delayed switch to ruxolitinib),” the researchers wrote.
Common adverse events in both groups were hypertension, thrombocytopenia, and thrombocytosis.
Passamonti F, Palandri F, Saydam G, et al. Ruxolitinib versus best available therapy in inadequately controlled polycythaemia vera without splenomegaly (RESPONSE-2): 5-year follow up of a randomised, phase 3b study. Lancet Haematol. 2022. doi:10.1016/S2352-3026(22)00102-8