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BCR-ABL1

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Also known as: BCR/ABL; bcr-abl Oncogene; Philadelphia Chromosome
Formal name: BCR-ABL1 Fusion

At a Glance

Why Get Tested?

To help diagnose and monitor the treatment of chronic myelogenous leukemia (CML) and a type of acute lymphoblastic leukemia (ALL)

When to Get Tested?

When you have results of a complete blood count (CBC) and/or signs and symptoms that suggest that you may have leukemia; periodically when you are being treated for CML or BCR-ABL1-positive ALL

Sample Required?

A blood sample drawn from a vein in your arm or a bone marrow sample collected using a bone marrow aspiration and/or biopsy procedure

Test Preparation Needed?

None

The Test Sample

What is being tested?

BCR-ABL1 refers to a gene sequence found in an abnormal chromosome 22 of some people with certain forms of leukemia. Unlike most cancers, the cause of chronic myelogenous leukemia (CML) and some other leukemias can be traced to a single, specific genetic abnormality in one chromosome. The presence of the gene sequence known as BCR-ABL1 confirms the diagnosis of CML and a form of acute lymphoblastic lymphoma (ALL).

Humans have 23 pairs of chromosomes containing inherited genetic information. Those genes contain the blueprints, in the form of DNA, for producing the proteins that our bodies rely on to function properly. While some genetic abnormalities are inherited, they can also come from changes that occur to genes or chromosomes after a person is born. This can happen through exposure to various environmental factors (e.g., radiation, certain chemicals) but more often for unknown reasons.

The BCR-ABL1 gene sequence is one such acquired change that is formed when pieces of chromosome 9 and chromosome 22 break off and switch places. When this occurs, the ABL1 region in chromosome 9 fuses with the BCR gene region in chromosome 22. This type of change is called a reciprocal translocation and is often abbreviated as t(9;22). The resulting chromosome 22 that has the BCR-ABL1 gene sequence is known as the Philadelphia (Ph) chromosome because that is where it was first discovered.

The resulting Philadelphia chromosome or BCR-ABL1 gene encode an abnormal protein that is responsible for the development of CML and a type of ALL. At diagnosis, 90-95% of cases of CML show a characteristic t(9;22) BCR-ABL1 reciprocal chromosomal translocation. About one in four adults with ALL have the translocation.

The protein formed by BCR-ABL1 is a type of enzyme called a tyrosine kinase. That enzyme is responsible for the uncontrolled growth of leukemic cells. When large numbers of abnormal leukemic cells start to crowd out the normal blood cell precursors in the bone marrow, signs and symptoms of leukemia start to emerge. Treatment of these leukemias typically involves a tyrosine kinase inhibitor (TKI).

Testing for BCR-ABL1 detects the Philadelphia chromosome and BCR-ABL1 fusion gene or its transcripts, which are the RNA copies made by the cell from the abnormal stretches of DNA. The presence of the BCR-ABL1 abnormality confirms the clinical diagnosis of CML, a type of ALL, and rarely acute myeloid leukemia (AML).

There are several different types of BCR-ABL1 tests available, including:

  • Cytogenetics (chromosome analysis or karyotyping)
    This test looks at chromosomes under a microscope to detect structural and/or numerical abnormalities. For example, the Philadelphia chromosome looks shorter than normal. Cells in a sample of blood or bone marrow are grown in the laboratory and then examined to determine if the Philadelphia chromosome is present. Other chromosomal abnormalities can also be detected.
  • Fluorescence in situ hybridization (FISH)
    This test method uses fluorescent dye-labeled probes to "light up" the BCR-ABL1 gene sequence when it is present. It can also determine the percentage of blood or bone marrow cells that contain the abnormal, fused BCR-ABL1 gene.
  • Genetic molecular testing (qualitative or quantitative)
    Polymerase chain reaction (PCR)-based qualitative and quantitative tests detect and measure the BCR-ABL1 gene in leukemia cells taken from blood or bone marrow samples.
  • Secondary mutations within the BCR-ABL1 are known to cause resistance to therapy. These can be detected by DNA sequencing methods.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm or a bone marrow sample is collected using a bone marrow aspiration and/or biopsy procedure.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

Common Questions

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Article Sources

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

Gregory J. Tsongalis, PhD, HCLD, CC. Professor of Pathology, Director, Molecular Pathology, Dartmouth Hitchcock Medical Center and Geisel School of Medicine at Dartmouth, Lebanon, NH.

BCR/ABL, mRNA Detection, Reverse Transcription-PCR (RT-PCR), Qualitative, Diagnostic Assay. Mayo Medical Laboratories. Available online at http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/83336 through http://www.mayomedicallaboratories.com. Accessed February 2014.

BCR/ABL, p210, mRNA Detection, Reverse Transcription-PCR (RT-PCR), Quantitative, Monitoring Chronic Myelogenous Leukemia (CML). Mayo Medical Laboratories. Available online at http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/89007 through http://www.mayomedicallaboratories.com. Accessed February 2014.

(Revised December 30 2013). How is Chronic Myeloid Leukemia Diagnosed? American Cancer Society. Available online at http://www.cancer.org/cancer/leukemia-chronicmyeloidcml/detailedguide/leukemia-chronic-myeloid-myelogenous-diagnosis through http://www.cancer.org. Accessed February 2014.

(Revised December 2013). Targeted Therapies for Chronic Myeloid Leukemia. American Cancer Society. Available online at http://www.cancer.org/cancer/leukemia-acutelymphocyticallinadults/detailedguide/leukemia-acute-lymphocytic-treating-targeted-therapy through http://www.cancer.org. Accessed February 2014.

(Updated: Jan 6, 2014) Besa E. Chronic Myelogenous Leukemia. Medscape Reference. Available online at http://emedicine.medscape.com/article/199425-overview#aw2aab6b2b2 through http://emedicine.medscape.com. February 2014.

(Revised 2013 July 10). What's New in Acute Lymphomatic Leukemia Research and Treatment? American Cancer Society. Available online at http://www.cancer.org/cancer/leukemia-acutelymphocyticallinadults/detailedguide/leukemia-acute-lymphocytic-new-research through http://www.cancer.org. Accessed February 2014.

Seiter, K. et al. (Updated 2014 Jan. 2). Acute Lymphoblastic Leukemia. eMedicine. Available online at http://emedicine.medscape.com/article/207631-overview through http://emedicine.medscape.com. Accessed February 2014.

Bessa, Emmanuel C. (Updated 6 January 2013). Chronic Myelogenous Leukemia. Medscape. Available online at http://emedicine.medscape.com/article/199425-overview through http://emedicine.medscape.com. Accessed February 2014.

(December 2013). BCR-ABL1 Quantitative Testing. Arup Laboratories. Available online at http://ltd.aruplab.com/Tests/Pdf/143 through http://ltd.aruplab.com. Accessed February 2014.

Sources Used in Previous Reviews

Besa, E. and Woermann, U. (Updated 2010 March 16). Chronic Myelogenous Leukemia. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/199425-overview through http://emedicine.medscape.com. Accessed September 2010.

Markman, M. (Updated 2009 August 26). Chronic Myeloid Leukemia and BCR-ABL. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/1723784-overview through http://emedicine.medscape.com. Accessed September 2010.

Leukemia - Chronic Myeloid (CML) Detailed Guide. American Cancer Society [On-line information]. Available online at http://www.cancer.org/Cancer/Leukemia-ChronicMyeloidCML/DetailedGuide/index through http://www.cancer.org. Accessed September 2010.

(Reviewed 2010 June 21). Targeted Cancer Therapies. National Cancer Institute Fact Sheet [On-line information]. Available online at http://www.cancer.gov/cancertopics/factsheet/Therapy/targeted through http://www.cancer.org. Accessed September 2010.

Mayo Clinic Staff (2008 November 13). Chronic myelogenous leukemia. MayoClinic.com [On-line information]. Available online at http://www.mayoclinic.com/health/chronic-myelogenous-leukemia/DS00564 through http://www.mayoclinic.com. Accessed September 2010.

Mayfield, E. (2009 October 20). Better Options for Children with Difficult-to-Treat Leukemia. NCI Cancer Bulletin v6 (20) [On-line information]. Available online at http://www.cancer.gov/ncicancerbulletin/102009/page2 through http://www.cancer.gov. Accessed September 2010.

Hazlehurst, L. et. al. (2009 August 25). Signaling Networks Associated with BCR-ABL–Dependent Transformation. Medscape from Cancer Control. 2009;16(2):100-107 [On-line information]. Available online at http://www.medscape.com/viewarticle/705840 through http://www.medscape.com. Accessed September 2010.

Chabner, B. and Chabner Thompson, E. (Revised 2009 July). Modalities of Cancer Therapy. Merck Manual for Healthcare Professionals [On-line information]. Available online at http://www.merck.com/mmpe/sec11/ch149/ch149b.html?qt=bcr-abl&alt=sh through http://www.merck.com. Accessed September 2010.

Ho, A. et. al. (Updated 2010 January). Chronic Myelogenous Leukemia – CML. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/CML.html?client_ID=LTD through http://www.arupconsult.com. Accessed September 2010.

Padmanabhan, S. et. al. (2008 July 15). Current Status of Therapy for Chronic Myeloid Leukemia: A Review of Drug Development. Medscape from Future Oncology 2008;4(3):359-377 [On-line information]. Available online at http://www.medscape.com/viewarticle/576209 through http://www.medscape.com. Accessed September 2010.

Mahadevan, D. (Updated 2010 January 3). Targeted Cancer Therapy. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/1372666-overview through http://emedicine.medscape.com. Accessed September 2010.

Esparza, S. et. al. (Updated 2009 February 27). Childhood Cancer, Genetics. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/989983-overview through http://emedicine.medscape.com. Accessed September 2010.

Merker, J. (2009 January 30). Use of Quantitative PCR in the Monitoring of Patients with Chronic Myelogenous Leukemia. CAP NewsPath [On-line information]. Available online through http://www.cap.org. Accessed September 2010.

Wang, J. (© 1996-2010). Chronic Myelogenous Leukemia: BCR/ABL. Specialty Laboratories [On-line information]. Available online at http://www.specialtylabs.com/books/display.asp?id=612 through http://www.specialtylabs.com/books. Accessed September 2010.

(© 1995-2010). Unit Code 83336: BCR/ABL, p190, mRNA Detection, Reverse Transcription-PCR (RT-PCR), Quantitative, Monitoring Assay. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/print.php?unit_code=83336 through http://www.mayomedicallaboratories.com. Accessed September 2010.

(© 1995-2010). Unit Code 89609: BCR/ABL, Tyrosine Kinase Inhibitor Resistance, Kinase Domain Mutation Screen. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/print.php?unit_code=89609 through http://www.mayomedicallaboratories.com. Accessed September 2010.

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