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.
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/or 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 minimal residual disease monitoring.
Quantitative PCR (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 e6a2, e8a2, e19a2 and e13a3/e14a3. Amongst CML patients, the major e13a2 or e14a2 transcript is the most frequent; whereas in Philadelphia positive Acute Lymphocytic Leukaemia (ALL) patients the minor e1a2 transcript is the most common BCR-ABL fusion (approx. 70-75%). Results from the 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 by use of a laboratory specific conversion factor.
Clinical Indications Molecular levels of BCR-ABL1 can be monitored at regular intervals for patients either on treatment with tyrosine kinase inhibitors or other therapeutic agents; post-transplantation; or off treatment.
Sample Required 20 mL peripheral blood or 3-5.0 mL bone marrow in EDTA (lavender top); 25uL of cDNA.
Sample Container EDTA
Sample Volume 10ml blood or 1ml bone marrow or 25uL cDNA
Transport/Storage Samples for post-diagnostic monitoring of CML must be less than 72 hours old upon receipt in the lab. PB samples >72 hours old will be rejected. Samples received in the lab after 3pm on a Friday afternoon will be rejected (unless they are taken on the same day). Diagnostic or pre-treatment samples are acceptable if within 5 days of collection.
Turnaround Time Major (e13a2/e14a2) and minor transcript (e1a2) within 10 working days; Rare transcripts within 20 working days.