Chronic Myeloid Leukemia BCR ABL

Fusion of BCR/ABL1 is observed in all patients with chronic myeloid leukemia (CML), in approximately 25% of adult patients with precursor B-cell acute lymphoblastic leukemia (B-ALL) and in 1% of patients with pediatric B-ALL. The chromosome mechanism resulting in BCR/ABL1 fusion is a t(9;22)(q34;q11.2) in approximately 85%, a complex 9;22 translocation with 1 or more additional chromosomes in approximately 15% and a chromosomally "cryptic" or insertional translocation in fewer than 1% of patients. Conventional cytogenetic studies are still the gold standard for identification of the t(9;22) and to monitor the effectiveness of treatment in post-therapy bone marrow specimens. FISH testing for BCR/ABL1 fusion or RT-PCR testing for p190 or p210 fusion forms are the recommended tests for evaluation of minimal residual disease following the disappearance of the t(9;22) in a post-treatment chromosome analysis. BCR/ABL1/ASS can be performed on bone marrow or peripheral blood and can be used to establish the percentage of neoplastic interphase nuclei for patients with CML at diagnosis and at all times during treatment, even in cytogenetic remission. BCR/ABL1/ASS can detect all known forms of the Ph chromosome, all atypical patterns associated with t(9;22)(q34q11.2) and can detect low levels of residual disease. We recommend BCR/ABL1/ASS at diagnosis subsequently to monitor the response to therapy.