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Test ID: MBCR    
BCR/ABL, Translocation 9;22, FISH (D-FISH)

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Useful For Suggests clinical disorders or settings where the test may be helpful

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 / Chromosome Analysis, Hematologic Disorders, Bone Marrow also be performed at initial diagnosis. Subsequently, D-FISH alone can be used to monitor the effectiveness of therapy.

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.

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.

Interpretation Provides information to assist in interpretation of the test results

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

Absent

100%

Minimal

67%-99%

Minor

33%-66%

Major

1%-32%

Complete

0%

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.

Supportive Data

D-FISH was tested in 2 investigations:

-In the first, we studied 65 bone marrow specimens from 35 normal subjects and from 30 patients with chronic myeloid leukemia (CML) or acute myeloid leukemia (ALL) with various kinds of Philadelphia (Ph) chromosomes. We also studied 37 bone marrow specimens collected from 10 patients before therapy and at least twice during therapy.

-In the second investigation, we studied 37 paired-sets of blood and bone marrow (collected within 24-96 hours of each other) from 10 patients before and after therapy. We studied 10 normal bone marrow specimens and 10 normal blood specimens.

 

For patients undergoing treatment, the results of D-FISH in blood and bone marrow correlated closely with quantitative chromosome analysis for bone marrow.  

 

The percentage of neoplastic nuclei in blood was usually lower than in bone marrow, but changes in percentage of neoplastic nuclei tracked closely in response to therapy.

 

Nuclei Analyzed

Abnormal Nuclei Cutoff

Percent Cutoff

500

>5

1.000%

1,000

>5

0.500%

1,500

>5

0.333%

2,000

>5

0.250%

2,500

>5

0.200%

3,000

>5

0.167%

3,500

>5

0.143%

4,000

>5

0.125%

4,500

>5

0.111%

5,000

>5

0.100%

5,500

>5

0.091%

6,000

>5

0.083%

 

Clinical Reference 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

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test