In myeloproliferative neoplasms (MPNs) and related disorders—including classical BCR, ABL1-negative MPNs, chronic myeloid leukemia (CML), and rarer entities such as chronic neutrophilic leukemia and hypereosinophilic syndromes—disease pathogenesis arises from a spectrum of somatic and structural genetic abnormalities and chronic inflammation, in which IFNs play a paradoxical role. Here, BCR is linked to chronic neutrophilic leukemia.