JAK2 and acquired polycythemia vera: Ruxolitinib is a JAK1/JAK2 inhibitor approved by the US Food and Drug Administration for patients with intermediate- or high-risk MF, including primary MF (PMF), post-polycythemia vera MF (PPV-MF), and post-essential thrombocythemia MF (PET-MF), as well as patients with PV who have had an inadequate response to or are intolerant of hydroxyurea [10].