JAK2 and Thrombocytosis: Essential thrombocythemia (ET) is one of four JAK2 mutation-prevalent myeloproliferative neoplasms (MPNs) and is characterized by a mandatory but not specific thrombocytosis (platelet count ≥450 × 109/L) that is proven or presumed to be clonal and not associated with another myeloid neoplasm, such as chronic myeloid leukemia (CML), polycythemia vera (PV), and primary myelofibrosis (PMF) [1, 2].