JAK2 and acquired polycythemia vera: Polycythemia vera (PV) is a chronic myeloproliferative neoplasm characterized by erythrocytosis, bone marrow hypercellularity, and activating Janus kinase (JAK) mutations (JAK2V617F or JAK2 exon 12 mutations) that is estimated to affect more than 100,000 people in the USA [1, 2].