BCR-ABL1 Qualitative and Quantitative Testing

  • Recommended when submitting initial diagnostic specimen for CML or Ph+ ALL when the BCR-ABL1 fusion form is not known (no previous BCR-ABL1 testing performed) or is unclear
  • If qualitative test is positive for the presence of the p210 (major breakpoint), p190 (minor breakpoint), or p230 (micro breakpoint), the corresponding quantitative test is performed
  • Appropriate for diagnosis and monitoring of individuals with CML or a subset of B-cell ALL
  • BCR-ABL1 major (p210) fusion form is present in almost all cases of CML and in a subset of ALL cases (e13a2 or e14a2 transcripts)

Useful in cases of Philadelphia chromosome positive (Ph+) ALL to quantify the BCR-ABL1 p190 fusion form

Related Tests
  • Useful for patients with an established diagnosis of a BCR-ABL1 positive (Ph+) leukemia to determine if a mutation is present that would interfere with response to TKI therapy in Ph+ ALL or CML
  • Detects all common mutations, including T315I
  • Provides higher sensitivity than traditional Sanger sequencing techniques
  • Offers coverage of SH2, SH3, and kinase domains

Assess for gene mutations, including substitutions and insertions and deletions that may have diagnostic, prognostic, and/or therapeutic significance

Recommended FISH panel for children with newly diagnosed ALL

Recommended FISH panel for adults with newly diagnosed ALL

  • Use to order individual or multiple oncology FISH probes if standard FISH panels are not desired
  • The specific probe for t(9;22); BCR-ABL1 must be requested

BCR-ABL1 quantitative testing is recommended for patients with either chronic myelogenous leukemia (CML), a hematopoietic stem cell disease, or acute lymphoblastic leukemia (ALL), an aggressive type of leukemia of either B- or T-lineage immature lymphoid cells. In CML, identification of BCR-ABL1 fusion genes is used for diagnosis and ongoing therapeutic monitoring. Massively parallel sequencing is used to identify gene mutations that may interfere with the effectiveness of tyrosine kinase inhibitor (TKI) therapy and to determine management strategy. In ALL, BCR-ABL1 fusion identification is used for risk stratification treatment decisions. Sequencing is used for minimal residual disease (MRD) assessment of Philadelphia chromosome positive (Ph+) ALL.

Typical Testing Strategy

Chronic Myelogenous Leukemia

  • Bone marrow cytogenetic studies and quantitative reverse transcription polymerase chain reaction (RT-PCR) measurement of BCR-ABL1 transcript levels recommended before treatment initiation
  • Quantitative RT-PCR is used to monitor response to TKI therapy
  • BCR-ABL1 kinase domain mutation analysis (massively parallel sequencing) is useful to monitor TKI therapy and disease progression

Acute Lymphoblastic Leukemia

  • Evaluation for the presence of recurrent genetic abnormalities at diagnosis using karyotyping and/or fluorescence in situ hybridization (FISH) assays
  • MRD assessment on bone marrow using flow cytometry and quantitative RT-PCR at the completion of therapy and at regular intervals to monitor progress

Disease Overview

Chronic Myelogenous Leukemia

Incidence

  • 1/555 in the U.S. 
    • Represents 15% of all adult leukemias 
  • Median age of onset is 67 years

Acute Lymphoblastic Leukemia

Incidence

1.58/100,000 in US 

  • 75-80% of acute leukemias in children
  • 20% of adult leukemias

Treatment Issues

The goal of TKI therapy is to achieve a complete cytogenetic response within 12 months of initiation of therapy with goal of eventual major molecular response. A subset of individuals will eventually achieve a complete molecular response (undetectable BCR-ABL1 transcripts using a test with 4.5 log sensitivity).

Prognostic Issues

A 3-log decrease in the level of BCR-ABL1 fusion transcripts (major molecular response) within 18 months of beginning TKI therapy is an indicator of favorable outcome. Monitoring for recurrence using quantitative measures is crucial for detecting early relapse.

Genetics

Gene

BCR-ABL1

Mutations

  • >130 mutations
  • Four regions tested
    • Adenosine triphosphate binding-loop (P-loop)
    • Drug-binding sites
    • Catalytic domain
    • Activation loop

Test Interpretation

BCR-ABL1, Major (p210), Quantitative

Analytical Sensitivity

1:125,000 normal cells (chart)

Results

Result Variant(s) Detected Interpretive Data

Positive

BCR-ABL1 fusion transcripts (p210) detected

BCR-ABL1/ABL1 quantitative ratio is provided (normalized copy number)

Results also reported in terms of BCR-ABL1 international scale (IS)

Weakly positive

BCR-ABL1 fusion transcripts detected below the limit of quantitation

BCR-ABL1 to ABL1 ratio cannot be calculated

IS result <0.0069%

Not detected

No BCR-ABL1 fusion transcripts detected

Does not exclude BCR-ABL1 fusion transcripts (p210) below the test limit of detection

Does not exclude BCR-ABL1 fusion transcripts not detected by this test (p190 or p230)

Limitation

Does not detect p190.

BCR-ABL1, Minor (p190), Quantitative

Analytical Sensitivity

1:125,000 normal cells (chart)s

Results

Result Variant(s) Detected Interpretive Data

Positive

BCR-ABL1 fusion transcripts (p210) detected

BCR-ABL1/ABL1 quantitative ratio is provided (normalized copy number)

Weakly positive

BCR-ABL1 fusion transcripts detected below the limit of quantitation

BCR-ABL1 to ABL1 ratio cannot be calculated

Not detected

No BCR-ABL1 fusion transcripts detected

Does not exclude BCR-ABL1 fusion transcripts (p190) below the test limit of detection

Does not exclude BCR-ABL1 fusion transcripts that are not detected by this test (p210 or p230)

References