Ruxolitinib is a potent and selective JAK1/JAK2 inhibitor7 that has demonstrated superiority over best available therapy (BAT) in the phase 3 Controlled Myelofibrosis Study with Oral JAK Inhibitor Treatment II (COMFORT-II) trial.8 Patients receiving ruxolitinib experienced rapid and durable reductions in splenomegaly, improved MF-related symptoms and quality of life measures, and prolonged overall survival (OS) compared with patients receiving BAT. Here, JAK1 is linked to myelofibrosis.