JAK1 and acquired polycythemia vera: In Europe, the JAK1/2 inhibitor ruxolitinib is licensed for the treatment of adult patients with primary myelofibrosis (PMF), post-PV MF (PPV-MF) or post-ET MF (PET-MF; [8]), as well as for patients with PV who are resistant or intolerant to hydroxyurea [9].