Unlike CML (single BCR/ABL1 positive entity, according to the WHO), diseases belonging to the group of BCR/ABL1 negative MPNs have been described, including polycythemia vera (PV), essential thrombocythemia (ET), primary myelofibrosis (PMF), chronic neutrophilic leukemia (CNL), chronic eosinophilic leukemia (CEL) and unclassifiable myeloproliferative neoplasms [10,11]. The gene discussed is ABL1; the disease is acquired polycythemia vera.