BCR::ABL1 (diagnostic and monitoring testing)

The BCR::ABL1 fusion gene is formed by a reciprocal translocation between chromosomes 9 and 22 [t(9;22)]. This reciprocal translocation forms an elongated chromosome 9 and a short chromosome 22, known as the Philadelphia chromosome. The Philadelphia chromosome harbours the aberrant BCR::ABL1 fusion gene that is detectable in around ~95% of chronic myeloid leukaemia (CML) cases, and, as such, is considered the hallmark diagnostic feature of the disease. However, this is not exclusive to CML and can be identified in around 30% of adult acute lymphocytic leukaemia (ALL) and some rare de novo acute myeloid leukaemia (AML) cases.

BCR::ABL1 screening:
As detection of BCR::ABL1 is diagnostic for CML and prognostic for ALL/AML, suspected patients should be tested for this fusion gene. For diagnostic purposes both cytogenetic studies (FISH and karyotype) and molecular studies (BCR::ABL1 multiplex PCR) should be performed.

The purpose of BCR::ABL1 multiplex PCR is to detect and identify the BCR::ABL1 transcript present resulting from the varying breakpoints in BCR and ABL1. This test is requested on all diagnostic samples as it is important that the fusion sub-type is determined prior to treatment to allow for accurate patient measurable residual disease monitoring.

Measurable residual disease (MRD) monitoring:
Reverse transcription quantitative PCR (RT-qPCR) is a method used to determine copy numbers of ABL1 and BCR::ABL1. We currently monitor individuals with major transcripts (e13a2/e14a2), minor transcripts (e1a2), and rare transcripts e1a3, e6a2, e8a2, e19a2 and e13a3/e14a3. Amongst CML patients, the e13a2/e14a2 transcript is the most frequent; compared to the e1a2 transcript in Philadelphia positive ALL patients. Results from the RT-qPCR assays are reported as a ratio between BCR::ABL1 and ABL1. The major e13a2 and/or e14a2 transcripts are also reported on the international scale (IS) by use of a laboratory specific conversion factor.

Click here to download the SIHMDS request form

• For the diagnosis of CML, or prognosis of ALL and AML patients. Please also request cytogenetic testing in these instances as the turnaround time is faster.

• For BCR::ABL1 MRD monitoring for patients either on treatment with tyrosine kinase inhibitors or other therapeutic agents; post-transplantation; or off treatment.

Please ensure the following information is provided to not cause a delay in testing:
• Suspected or known diagnosis
• BCR::ABL1 transcript type if known
• Current therapy
• Reason for referral

Diagnostic, pre-treatment, relapse or TKD samples must be less than 5 days old upon receipt within the laboratory.

The laboratory is not UKAS accredited for minor (e1a2) or rare transcript RT-qPCR testing. The minor (e1a2) RT-qPCR is awaiting assessment.