A chronic myeloproliferative neoplasm characterized by the expression of the BCR-ABL1 fusion gene. It presents with neutrophilic leukocytosis. It can appear at any age, but it mostly affects middle aged and older individuals. Patients usually present with fatigue, weight loss, anemia, night sweats, and splenomegaly. If untreated, it follows a biphasic or triphasic natural course; an initial indolent chronic phase which is followed by an accelerated phase, a blast phase, or both. Allogeneic stem cell transplantation and tyrosine kinase inhibitors delay disease progression and prolong overall survival.