ABL1 and essential thrombocythemia: Myeloproliferative disorders (MPDs) are an example of phenotypic and functional MSC heterogeneity in disease, which include chronic myeloid leukemia (CML) and BCR-ABL-negative myeloproliferative neoplasms (MPNs), such as polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) (Arber et al., 2016).