LAUSR

Myeloproliferative neoplasms (MPNs) are clonal hematopoietic stem cell disorders characterized by the expansion of myeloid lineage cells. Chronic myeloid leukemia (CML) is characterized by a BCR-ABL1 fusion gene that causes constitutive tyrosine kinase activity. Polycythemia vera, essential thrombocythemia, and primary myelofibrosis (PMF) are frequently associated with driver mutations in genes such as JAK2, CALR, and MPL and are mutually exclusive of BCR-ABL1. Herein, we report the first case study of a patient diagnosed with accelerated-phase CML while undergoing treatment for initial JAK2 V617F-positive, BCR-ABL1-negative PMF. This finding emphasizes the importance of BCR-ABL1 testing in patients with an atypical BCR-ABL1-negative MPN disease course.