Polycythemia vera is a chronic myeloproliferative disorder characterized by increased red blood cells, blood volume, and often leukocytosis and thrombocytosis. The bone marrow is hypercellular with increased myeloid, erythroid, and megakaryocyte cells. A common genetic mutation involves the JAK2 gene, resulting in continuously activated tyrosine kinase signaling and driving cell proliferation. A JAK2 V617F mutation is present in the majority of polycythemia vera patients.