JAK1 and myelofibrosis: The Janus kinase 1 (JAK1)/JAK2 inhibitor ruxolitinib, which has been shown to provide effective and lasting spleen size reduction and symptom mitigation as well as a survival advantage compared with placebo and best available therapy in randomized controlled clinical trials, has been approved for the treatment of myelofibrosis in more than 80 countries worldwide.