FeedbackReverse Transcription Polymerase Chain Reaction
- Recommended when submitting initial diagnostic specimen for CML or ALL when the BCR::ABL1 fusion form is not known (no previous BCR::ABL1 testing performed) or is unclear
- If the qualitative test is positive for the presence of the common fusions transcripts of p210 (major breakpoint) or p190 (minor breakpoint), then the corresponding quantitative test is performed.
Reverse Transcription Polymerase Chain Reaction
- Appropriate for the monitoring of individuals with CML or Ph+ 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)
Quantitative Reverse Transcription Polymerase Chain Reaction
Appropriate for monitoring of individuals diagnosed with Ph+ ALL or CML to quantify the BCR::ABL1 p190 fusion form
See Related Tests
BCR::ABL1 (BCR-ABL1) quantitative testing is recommended for patients with either chronic myeloid 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. In ALL, BCR::ABL1 fusion identification and quantification are used for risk stratification and treatment decisions. BCR::ABL1 fusion quantification is used for minimal residual disease (MRD) assessment of Philadelphia chromosome positive (Ph+) ALL.
Massively parallel sequencing (MPS) is used to identify mutations that may interfere with the effectiveness of tyrosine kinase inhibitor (TKI) therapy and to further inform the management strategy in CML and a subset of ALL patients.
Typical Testing Strategy
Chronic Myeloid Leukemia
- Bone marrow cytogenetic studies and qualitative reverse transcription polymerase chain reaction (RT-PCR) and quantitative RT-PCR (qRT-PCR) measurement of BCR::ABL1 transcript levels are recommended before treatment initiation.
- qRT-PCR is used to monitor response to TKI therapy and detection of MRD.
- BCR::ABL1 kinase domain variant analysis (MPS) is useful to detect variants which result in resistance to TKI therapy and is commonly seen in disease progression and refractory diseases.
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 qRT-PCR at the completion of therapy and at regular intervals to monitor progress
Disease Overview
Chronic Myeloid Leukemia
Incidence
- 2.6/100,000 in the United States
- Represent 15% of all adult leukemias
- Median age of onset is 67 years
Acute Lymphoblastic Leukemia
Incidence
- 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 the goal of eventual major molecular response (BCR::ABL1 transcripts below 0.1% IS, MR3.0). A subset of individuals will eventually achieve a deep or complete molecular response (BCR::ABL1 transcripts below 0.0032% international scale [IS], MR4.5).
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 a favorable outcome. Monitoring for recurrence using quantitative measures is crucial for detecting MRD and early relapse.
Genetics
Gene
BCR::ABL1 (BCR-ABL1)
Variants
- >130 variants
- Four regions tested
- Adenosine triphosphate binding-loop (P-loop)
- Drug-binding sites
- Catalytic domain
- Activation loop
Test Interpretation
BCR-ABL1, Major (p210), Quantitative
Analytic Sensitivity
Limit of detection: 0.0032% IS
Results
| Result | Variant(s) Detected | Interpretive Data |
|---|---|---|
|
Detected |
BCR::ABL1 fusion transcripts (p210) detected |
BCR::ABL1 IS is reported |
|
Detected above LOQ |
BCR::ABL1 fusion transcripts (p210) detected above LOQ |
BCR::ABL1 IS is above 50% |
|
Weakly positive |
BCR::ABL1 fusion transcripts detected below the limit of quantitation |
BCR::ABL1 to ABL1 IS result is between 0.002% to 0.0032%, cannot be quantified |
|
Not detected |
No BCR::ABL1 fusion transcripts detected |
Does not exclude BCR::ABL1 fusion transcripts (p210) below the test limit of detection (IS below 0.002%) Does not exclude BCR::ABL1 fusion transcripts not detected by this test (p190 or p230) |
|
LOQ, limit of quantification |
||
Limitation
Does not detect p190, p230, or rare variants of p210 forms
BCR-ABL1, Minor (p190), Quantitative
Analytic Sensitivity
1:125,000 normal cells (chart)
Results
| Result | Variant(s) Detected | Interpretive Data |
|---|---|---|
|
Positive |
BCR::ABL1 fusion transcripts (p190) detected |
BCR::ABL1/ABL1 quantitative ratio is provided by an NCN |
|
Weakly positive |
BCR::ABL1 fusion transcripts (p190) detected below the limit of quantitation |
BCR::ABL1 to ABL1 NCN ratio cannot be calculated |
|
Not detected |
No BCR::ABL1 fusion (p190) 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) |
|
NCN, normalized copy number |
||
Limitation
Does not detect p230 or p210
References
-
NCCN - Chronic myeloid leukemia v2.2021
National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology: Chronic myeloid leukemia. Version 2.2021. [Updated: Feb 2021; Accessed: Sept 2022]
-
NCCN - Acute lymphoblastic leukemia v2.2021
National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology: Acute lymphoblastic leukemia. Version 2.2021. [Updated Feb 2021; Accessed: Sept 2022]