In the last several years, oral small molecule tyrosine kinase inhibitors of JAK2 have been tested in both pre-clinical and clinical trials of patients with MPNs including PV/ET. These agents have demonstrated remarkable responses in terms of reduction in splenomegaly and correction of leukocytosis, erythrocytosis, and thrombocytosis. However, mature follow up of PV patients treated with JAK2 inhibitors evaluating reduction in thrombotic risk and evolution to MF is not known. Currently, Ruxolitinib (Jakafi) is being evaluated in a phase III study in patients with high risk PV that are refractory/intolerant to hydroxyurea [Response trial: NCT01243944].