JAK2 and primary myelofibrosis: In 2008, the World Health Organization incorporated genetic tests for the gene of Janus kinase 2 (JAK2) V617F mutation and other functionally similar mutations (such as JAK2 exon 12 mutations) into the diagnostic criteria for myeloproliferative neoplasms (MPN), a collection of hematological malignancies that include polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis [1].