Despite the acquired somatic unique JAK2 V617F mutation being responsible for the development of MPN in 60% of patients with essential thrombocythemia (ET), and 55% of patients with MF, mutations (+1 frameshifts) in calreticulin (mutCALR) are the second most prevalent and occur in 25% and 35% of patients diagnosed with ET and MF, respectively [94, 95, 96]. Here, CALR is linked to essential thrombocythemia.