Tofacitinib, acting on JAK1, JAK2 and JAK3 has been authorized to treat rheumatoid arthritis, psoriatic arthritis and ulcerative colitis; baricitinib, exhibiting high affinity for JAK1 and JAK2, has been authorized for rheumatoid arthritis; ruxolitinib, with a similar spectrum of baricitinib, gained market authorization to treat myelofibrosis. Here, JAK2 is linked to myelofibrosis.