JAK2 and essential thrombocythemia: In addition, Guglielmelli et al. [85] prospectively measured changes in JAK2 and CALR VAF in 77 PV or ET patients treated with ruxolitinib, reporting reductions from a median of 68% to 3.5% in JAK2-mutated cases and from 49% to 4% in a CALR-mutated ET patient.