JAK2 and essential thrombocythemia: In 2007, JAK2 exon 12 mutations, particularly in‐frame insertions or deletions between codons 536 and 544, were discovered in JAK2 V617F‐negative PV patients [23, 24]; JAK2 exon 12 mutations were also detected in post‐PV MF cases, not in ET, post‐ET MF, and PMF cases [23].