BCR and acquired polycythemia vera: Moreover, among these, the distinction was made between ‘classical BCR::ABL1-negative MPN’, characterized by a Janus Kinase (JAK) protein deregulation and including Polycythemia Vera (PV), Essential Thrombocythemia (ET), Primary Myelofibrosis (PMF) and other BCR::ABL1-negative MPN including Chronic Neutrophilic Leukemia (CNL), Chronic Eosinophilic Leukemia (CEL), not otherwise specified, Hypereosinophilic Syndrome (HES), Chronic myeloproliferative neoplasm unclassifiable and Mast cell disease [7].