JAK2 and essential thrombocythemia: This mutation occurs in up to one-third of patients with benign PVT and healthy livers.13,14 A proportion of patients with JAK2 mutations develop myeloproliferative neoplasms (MPN), which are characterized by the proliferation of stem cells such as mature granulocytes (primary myelofibrosis), red blood cells (polycythemia vera), and/or platelets (essential thrombocythemia).15