All these clonal markers are formally integrated into the WHO diagnostic criteria for PV (98% JAK2 mutational frequency), ET (60% JAK2, 22% CALR and 3% MPL) and PMF (58% JAK2, 25% CALR and 7% MPL); about 10–15% of patients with PMF or ET lack all the three driver mutations and are generally referred to as “triple negative” [7,17]. Here, JAK2 is linked to essential thrombocythemia.