BCR/ABL, Translocation 9;22, FISH (D-FISH)
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
A proliferation of cells with a t(9;22)(q34;q11.2) occurs in the bone marrow and peripheral blood of more than 90% of patients with chronic myeloid leukemia (CML); in approximately 6% of children and 17% of adults with acute lymphoblastic leukemia (ALL); and approximately 1% of patients with acute myeloid leukemia (AML) with immature granulocytes.
The abnormal chromosome 22 derived from this translocation is called the Philadelphia (Ph) chromosome.
The remaining 10% of patients with CML have a variant Ph chromosome.
The classic Ph and all variants result in fusion of part of the Abelson (ABL1) oncogene from 9q34 with the breakpoint cluster region (BCR) at 22q11.2.
Conventional cytogenetic studies are widely used to quantify disease and to monitor the effectiveness of treatment for patients with CML; especially those on interferon or Gleevec/lmatinib mesylate therapy.
Considerable evidence shows a strong correlation between changes in percentage of Ph-positive metaphases after therapy and response to therapy.
The best outcome for survival and prolonged chronic phase appears to be in patients with CML in whom the percentage of Ph-positive metaphases is no longer detectable by conventional cytogenetics. When this happens, the patient is in cytogenetic remission.
This test offers a highly sensitive method using FISH and DNA probes for ABL1 and BCR for quantifying nonproliferating neoplastic cells with BCR and ABL1 fusion.
D-FISH (dual) ffusion FISH is a testing strategy that uses 2 fluorescent probes to identify and differentiate between the classic and variant Ph chromosomes by detecting double BCR and ABL1 fusion in cells with a t(9;22)(q34;q11.2): 1 on the abnormal chromosome 9 and 1 on the Ph chromosome.
Establishing the percentage of neoplastic interphase nuclei for patients with chronic myeloid leukemia (CML) at diagnosis and at all times during treatment, even in cytogenetic remission
Detecting all known forms of the Philadelphia (Ph) chromosome
Identifying and monitoring of the Ph chromosome in patients with CML, acute lymphocytic leukemia (ALL), or acute myeloid leukemia (AML)
It is recommended that conventional chromosome analysis (BM/8506 Chromosome Analysis, for Hematologic Disorders, Bone Marrow) also be performed at initial diagnosis. Subsequently, D-FISH alone can be used to monitor the effectiveness of therapy.
Specimens that contain > or =1% neoplastic nuclei with BCR and ABL1 fusion have a high likelihood of having a clone with t(9; 22) (q34; q11.2) or a variant of this anomaly.
Specimens with <1% interphase nuclei with BCR and ABL1 fusion may have minimal residual disease or do not have a neoplasm involving BCR and ABL1 fusion.
The normal range for interphase nuclei in blood and bone marrow is < or =5 cells when scoring between 500 and 6,000 nuclei. See Supportive Data.
D-FISH can detect >1% disease when 500 interphase nuclei are scored and >0.079% disease when 6,000 nuclei are scored.
To monitor the effectiveness of therapy, it is useful to divide the percentage of neoplastic cells after therapy by the percentage of neoplastic cells before treatment. Many clinicians use this calculation to classify the patient's response to therapy according to the table below.
Cytogenetic Response to Therapy
Percent Neoplastic Nuclei Post-treatment Relative to Pretreatment
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Conventional cytogenetic analysis should be performed at initial diagnosis.
D-FISH does not detect cytogenetic or molecular genetic anomalies other than BCR and ABL1 fusion.
Some patients with chronic myeloid leukemia may have a chromosome abnormality that produces an atypical D-FISH pattern not consistent with classical BCR/ABL1 fusion. The sensitivity of D-FISH for these patients varies depending on the nature of the chromosome anomaly and has not been established. Special scoring criteria will be established by examining metaphases with D-FISH to quantify disease in these patients.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
An interpretive report will be provided.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Dewald GW, Wyatt WA, Silver RT: Atypical BCR and ABL D-FISH patterns in chronic myeloid leukemia and their possible role in therapy. Leuk Lymphoma 1999;34(5-6):481-491
2. Dewald GW, Juneau AL, Schad CR, Tefferi A: Cytogenetic and molecular genetic methods for diagnosis and treatment response in chronic granulocytic leukemia. Cancer Genet Cytogenet 1997;94:59-66
3. The Italian Cooperative Study Group on Chronic Myeloid Leukemia: Interferon alpha-2a as compared with conventional chemotherapy for the treatment of chronic myeloid leukemia. N Engl J Med 1994;330:820-825
4. Dewald GW: Interphase FISH studies for chronic myeloid leukemia. In Methods in Molecular Biology. Vol 204. Molecular Cytogenetics: Protocols and Applications. Edited by YS Fan. Totowa, NJ, Humana Press, USA, 2002 pp 311-342