In contrast, patients with BCR::ABL1-negative MPNs (PV, ET, prefibrotic PMF, and overt PMF) transform to other subgroups with a 10–15% frequency and share common gene mutations, namely JAK2 mutations (V617F and exon 12), MPLW515L/K, and CALR exon 9 frameshift mutations, in a mutually exclusive manner [3,4,5,6,7,8,9]. Here, CALR is linked to essential thrombocythemia.