ABL1 and acquired polycythemia vera: According to the fifth edition of the World Health Organization (WHO) criteria, MPNs include chronic myeloid leukemia (CML), which is defined by the presence of the Philadelphia chromosome and BCR::ABL1 fusion gene, polycythemia vera (PV), essential thrombocythemia (ET), primary myelofibrosis (PMF), chronic neutrophilic leukemia (CNL), chronic eosinophilic leukemia (CEL), juvenile myelomonocytic leukemia, and myeloproliferative neoplasms, not otherwise specified.