JAK2 and myelofibrosis: Up to 90% of patients with myelofibrosis harbor somatic mutations in the driver genes JAK2, CALR, or MPL, resulting in constitutive activation of the Janus kinase (JAK)‐signal transducer and activator of transcription (STAT) signaling pathway, most commonly gain‐of‐function JAK2 V617F mutation [3, 4, 7].