Klampfl et al. examined somatic mutations of MPNs, essential thrombocythemia (ET), polycythemia vera (PV) and primary myelofibrosis (PMF) by whole-exome sequencing (WES) and identified mutations to MPL and CALR in addition to JAK2 V617F in ET and PMF.7 Another group reported the presence of somatic mutations in MPNs, with the JAK2 mutation being the most frequent, followed by the CALR mutation.8 In addition to JAK2 and CALR, somatic mutations were also identified in TET2, DNMT3A, ASXL1, and EZH2 in MPN patients. Here, CALR is linked to acquired polycythemia vera.