JAK2 and primary myelofibrosis: Primary myelofibrosis (PMF) is a clonal myeloproliferative neoplasm (MPN) stemming from hematopoietic stem and progenitor cells (HSPCs), frequently associated with mutations in Janus kinase signal transducer (JAK2), calreticulin (CALR), or thrombopoietin receptor (MPL).