CALR and essential thrombocythemia: However, the distribution and the percentage of the 3 driver mutations in these 54 ET patients were comparable with most studies: 27 (50%) patients harbored the JAK2V617F mutation, 1 (1.9%) patient with the MPLW515K mutation, 19 (35.2% overall and 68.2% in JAK2/MPL-unmutated cases) patients with CALR exon 9 mutations, and 7 (13%) TN patients.