JAK1 and myelofibrosis: Ruxolitinib is a potent and selective oral JAK1 and JAK2 inhibitor that was FDA-approved in 2011 for the treatment of myelofibrosis (MF), post-polycythemia vera myelofibrosis (PPV-MF), and post-essential thrombocythemia myelofibrosis (PET-MF) [30–32].