In patients with polycythemia vera (PV) and essential thrombocythemia (ET) refractory or intolerant to hydroxyurea, use of the JAK1/JAK2 inhibitor, INCB018424, results in rapid and durable clinical benefits, including normalization of hematologic parameters, resolution of splenomegaly, and alleviation of symptoms, long-term follow-up data from an ongoing open-label phase 2 study have found. The data was presented at the 52nd American Society of Hematology Annual Meeting and Exposition.