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MOLECULAR Analysis:
Bcr/Abl Gene Rearrangement (t 9;22), Quantitative RT-PCR Assay
The 9;22 Philadelphia chromosome translocation is found in approximately 95% of patients with chronic myelogenous leukemia (CML), 10-25% of adult patients with acute lymphocytic leukemia (ALL), 5% of children with ALL, and occasionally in patients with acute myelogenous leukemia (AML). This translocation is the result of the transposition of the Abl proto-oncogene from chromosome 9 to the Bcr (breakpoint cluster region) gene on chromosome 22. The Bcr/Abl fusion gene forms one to three distinct chimeric mRNAs, depending on the specific breakpoint in the Bcr gene. The fusion mRNA in CML patients results from breakpoints in M-Bcr (major breakpoint cluster region) exon 2 or 3 and fusion to Abl exon II (b2a2, b3a2). The fusion mRNA in the majority of ALL patients results from a breakpoint in m-Bcr (minor breakpoint cluster region) exon 1 and fusion to Abl exon II (e1a2). Some ALL patients have breakpoints in M-Bcr which are identical to those breakpoints found in CML patients.
- Confirm the presence of Bcr/Abl fusion transcripts in patients with CML or ALL prior to treatment
- Monitor Bcr/Abl transcript levels in patients with CML or ALL, particularly those who have achieved a complete cytogenetic response
Our testing methodology involves real time quantitative reverse transcriptase polymerase chain reaction (Q-RT-PCR). Total RNA is extracted and reverse transcribed to cDNA. Real time PCR is performed to measure the quantity of Bcr/Abl fusion transcripts resulting from breakpoints in M-Bcr (b3a2 and b2a2) and m-Bcr (e1a2). An additional amplification of a G6PDH gene segment is also performed as a control for RNA quality and as a reference for relative quantification. Bcr/Abl and G6PDH transcripts are quantified by comparison to a standard curve.
In our laboratory, the analytic sensitivity of this quantitative assay is at least 1 in 100000.
The results from this assay should always be interpreted in the context of morphologic and other relevant data. The results should not be used alone for a diagnosis of malignancy.
Blood: 5 cc collected in a purple top (EDTA) or yellow top (acid citrate dextrose) vacutainer tube. Do not centrifuge or freeze. Specimen should be stored in the refrigerator and transported with a cold pack or on wet ice. Specimen should reach the laboratory within 48 hours of collection.
Bone marrow: 1 - 2 cc collected in a purple top (EDTA) or yellow top (acid citrate dextrose) vacutainer tube. Do not centrifuge or freeze. Specimen should be stored in the refrigerator and transported with a cold pack or on wet ice. Specimen should reach the laboratory within 48 hours of collection.
7 - 10 days
83891, 83896 (4x), 83898 (2x), 83902, 83912, 83913
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