Frequency of JAK2, CALR, and MPL mutations in PV, ET, and MF.JAK2 mutations are found in 97% of patients with PV and in 50%–60% of those with ET and MF. CALR mutations are the next most frequent genetic aberration, affecting 1/3 of patients with ET or MF. MPL mutations are found in 3%–10% of ET or MF patients. JAK2, MPL, and CALR mutations are mutually exclusive in the majority of patients. Ten to fifteen percent of ET and MF cases have no common underlying genetic marker.