JAK2 and essential thrombocythemia: While the most common JAK2 V617F mutation is found in around 95% of PV patients and 60% of ET and MF patients, about 15%–25% of ET and 25%–36% of MF patients carry CALR mutations, and 4%–9% of ET and MF patients carry MPL mutations.3, 4, 5, 6