BCR and chronic myelogenous leukemia, BCR-ABL1 positive: The BCR-ABL1 fusion protein is the hallmark of Chronic Myeloid Leukemia (CML)14,15, but it is also a frequent cytogenetic abnormality in precursor B-lymphoblastic leukemia (B-Acute Lymphoblastic Leukemia, B-ALL) found in adults16 and, more rarely, in pediatric patients17.