Essential thrombocythemia (ET), polycythemia vera (PV), and primary myelofibrosis (PMF) are a group of Philadelphia (Ph)-negative myeloproliferative neoplasms (MPN) characterized by overlapping clinical and laboratory features, as well as common phenotypic driver mutations in the JAK2, CALR and MPL tyrosine kinase genes. This evidence concerns the gene CALR and acquired polycythemia vera.