Analysis of 639 patients with ET and 323 with PV by Vannucchi et al. reported an increased risk of thrombosis (both arterial and venous) in the small percentage of ET patients who were homozygous for JAK2V617F (hazard ratio 3.97, 95% confidence interval [CI] 1.34–11.7) compared with JAK2 wild-type patients [66]. Here, JAK2 is linked to essential thrombocythemia.