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BCR/ABL Minor Quant


Test Information

Test Name: BCR/ABL Minor Quant

Performing Lab: Molecular Diagnostic

Synonyms: Minor t9;22
t(9;22) Minor by PCR

Order Includes: Minor t(9;22) Translocation by PCR

Turnaround Time: 14 days

Additional Interpretation: Confirm suspected diagnosis of ALL, monitoring of minimal residual disease with chemotherapies and after bone marrow transplantation by detection of the m-bcr, P190 specific transcript.

The Philadelphia (Ph) chromosome [t(9
22)(q34q11)], a cytogenetic aberration that results from a reciprocal translocation that joins 3' sequences of the thyrosine kinase c-ABL protooncogene on chromosome 9 to 5' sequences of the BCR gene on chromosome 22, is found in about 20% to 30% of all adult patients with acute lymphoblastic leukemia (ALL). The majority (approximately 70% to 75%), of Ph breakpoints in ALL occur in the first intron of the BCR gene, which is referred to as the minor breakpoint cluster region, and results in the fusion of BCR exon 1 to ABL exon 2. This fusion produces a 7.0 kb BCR-ABL transcript (e1a2 BCR-ABL) that encodes a 190 kDa protein. In approximately 25% to 30% of adult patients with Ph-positive ALL, the breakpoint occurs in the 5.8 kb major breakpoint cluster region of the BCR gene. The BCR-ABL fusion gene produces an 8.5 kb BCR-ABL transcript (b2a2 or b3a2 BCR-ABL) that encodes a protein of 210kda.

pH-positive ALL is an aggressive disease with a poor prognosis and is consequently resistant to conventional chemotherapy. Although conventional chemotherapy includes hematological complete remissions (CR) in approximately 70% of these patients, the relapse rate is high and the 5-year leukemia free survival rate is less than 15%. Thus, pH-positive ALL patients are candidates for more aggressive chemotherapies, including bone marrow transplantation (BMT). However, the relapse rate is high even after BMT, ranging from 40% to 80%.

Inadequate quantity or quality of the specimen can result in amplification failure. This assay detects only the minor transcript encoding for the P190 protein, arising from the e1a2 bcr-abl t(9
22) translocation. The b2a2 and b3a2 transcripts encoding for the P210 protein, arising from the Major-bcr t(9
22) translocation and the 5-bcr, P230 specific transcript, are not detected by this assay.

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Methodology: This assay uses a TaqMan® reverse-transcription PCR (TaqMan® RT-PCR) from patient total RNA to detect and quantitate the transcripts arising from the t(9
22) translocation encoding for the P190 protein and the normal bcr transcript. These transcripts are reverse transcribed and amplified in a single step TaqMan® RT-PCR reaction and detected by the ABI PRISM® 7500 Sequence Detection System. The TaqMan® assay involves a probe labeled with a reporter fluorescent dye on the 5' end (FAM for the e1a2 probe and VIC for the normal bcr probe) and a quencher dye (TAMRA) on the 3' end. TAMRA quenches FAM/VIC fluorescence when they are in the molecular proximity, such as in both ends of the probe. The amount of specific amplicon is inferred by the reporter dye fluorescence released by the 5' to 3' exonuclease activity of the Taq DNA polymerase, from the specific dually labeled probe.

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CPT Code: 81207

 

 

Result Information

No Information Available

 

 

Specimen & Collection Information

Specimen Name: Whole Blood
Bone Marrow

Container Type: Lavender Top (EDTA)

Special Handling: Room Temperature

Specimen Volume: (Whole Blood) Lavender Top: 2.0 mL (Bone Marrow) Lavender Top: 0.5 mL

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Specimen Transportation & Storage Information

Storage and Transport:Blood and Bone Marrow:
Deliver to the lab immediately for processing. Keep at room temperature. Remote Locations : Blood and Bone Marrow:
Deliver to the lab immediately for processing. Do not spin. Keep at room temperature.