JAK2 and acquired polycythemia vera: Nowadays, other similar molecules are under clinical trials, such as ruxolitinib, which is a selective inhibitor of the Janus kinase 1 (JAK1) and Janus kinase 2 (JAK2) enzymes, approved by the FDA for the treatment of post-essential thrombocythemia myelofibrosis, post-polycythemia vera myelofibrosis, high- and intermediate-risk myelofibrosis and refractory polycythemia vera [182].