Chronic myeloproliferative diseases were classified into essential thrombocytosis (ET), primary myelofibrosis (PM), chronic neutrophilic leukemia, chronic eosinophilic leukemia, chronic myeloid leukemia (CML), and unclassified myeloproliferative neoplasia by WHO in 2016.12JAK2, CALR, and MPL are driver mutations. Here, CALR is linked to essential thrombocythemia.