Compared to JAK2 V617F-positive PV patients, those with exon 12 mutations had significantly higher hemoglobin levels, reduced serum erythropoietin levels, and lower platelet and leukocyte counts at diagnosis, but a similar incidence of thrombosis, myelofibrosis, leukemia, and death [38]. Here, JAK2 is linked to myelofibrosis.