In chronic myeloid leukemia (CML), fusion of the breakpoint cluster region (BCR) on chromosome 22 with the Abelson murine leukemia viral oncogene homolog 1 (ABL) tyrosine kinase of chromosome 9, results in the fusion gene BCR-ABL1. The gene discussed is BCR; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.