The myeloproliferative neoplasms (MPNs), essential thrombocytosis (ET), polycythemia vera (PV), and primary myelofibrosis (PMF) share the same acquired genetic lesion, JAK2 V617F, which may explain shared tendencies towards cardinal complications, which include thrombosis, extramedullary hematopoiesis, evolution between phenotypes, and leukemic transformation. Here, JAK2 is linked to essential thrombocythemia.