CALR and acquired polycythemia vera: MPN are categorized into various subentities, such as essential thrombocythemia (ET), polycythemia vera (PV) and primary myelofibrosis (PMF), which harbor these mutations at different frequencies [2], with JAK2 V617F mutations occurring in almost all PV cases but only approximately 50–60% ET and PMF cases, CALR mutations occurring in 25–35% of ET and PMF but not PV cases, and MPL mutations occurring in 5–8% of ET and PMF but not PV cases [3].