JAK1 and acquired polycythemia vera: The Randomized Study of Efficacy and Safety in Polycythemia Vera With JAK Inhibitor INCB018424 Versus Best Supportive Care (RESPONSE) is a global, multicenter, open-label, phase 3 trial comparing the efficacy and safety of the JAK1/JAK2 inhibitor ruxolitinib with best available therapy (BAT) in patients with PV who are resistant to or intolerant of hydroxyurea [4].