Myeloproliferative neoplasms (MPNs), polycythemia vera (PV), essential thrombocytosis (ET), and primary myelofibrosis (PMF) are an unusual group of myeloid neoplasms since they share three gain-of-function somatic driver mutations, JAK2, CALR and MPL, and, as a consequence, there is an inappropriate increase in the production of morphologically and functionally normal red cells, leukocytes, and platelets either together or alone, depending on the particular MPN. Here, CALR is linked to essential thrombocythemia.