CALR and essential thrombocythemia: Three different types of molecular markers are known in MPNs: activating mutations in the JAK2gene (JAK2V617F being the most frequent mutation, found in all subtypes of MPNs); activating mutations in theMPL gene (MPLW515L/K mostly, detected only in ET and PMF); and diverse alterations of the gene encoding calreticulin (CALR), also typical of ET and PMF (Figure 2, Table 1) [53,54,55,56,57,58,59,60,61].