Lab Test

Chronic Myelogenous Leukemia BCR/ABL1 Fusion by Fluorescence In Situ Hybridization (FISH) Analysis

FISH, GBCRF, Philadelphia Chromosome, BCR/ABL1, genetic, BCR/ABL1 fusion for t(9;22)(q34;q11.2) detection, BCR/ABL1 + ASS gene

Test Codes


Specimen Collection Criteria

Collect: Peripheral blood or bone marrow aspirate in a Green-top Sodium Heparin tube. (Minimum: 1.0 mL)

A copy of the requisition must be sent with the specimen.

Physician Office/Draw Specimen Preparation

Do not freeze specimen. Maintain specimens at room temperature (20-25°C or 68-77°F) prior to courier pickup. For delays in transport (greater than 48 from the time of collection), refrigerate (2-8°C or 36-46°F) the specimen.

Preparation for Courier Transport

Transport: Peripheral blood or bone marrow, at room temperature (20-26°C or 68-78.8°F) or refrigerated (2-8°C or 36-46°F).

Rejection Criteria

Specimens arriving in the laboratory 4 days or more following the original collection date.

Fixed or frozen specimens. 

In-Lab Processing

Specimens are processed immediately upon receipt in the Laboratory.


Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): 48 hours
Refrigerated (2-8°C or 36-46°F): 96 hours
Frozen (-20°C/-4°F or below): Unacceptable

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days. A backup cell pellet is maintained for two weeks after the case has been signed out.


Royal Oak Cytogenetics Laboratory


Monday – Friday, 8:00 am – 5:00 pm.
Results available within 7 days of receipt in the Laboratory.

Reference Range

Positive or negative for a neoplastic clone. An interpretative report will be provided.

Test Methodology

Fluorescence In Situ Hybridization (FISH) Analysis.


A positive FISH result indicates the presence of the Philadelphia chromosome and the t(9;22)(q34;q11.2). In the routine monitoring of CML patients, reverse transcriptase polymerase chain reaction (RT-PCR) is the most sensitive method for identifying a very small clone of cells with a BCR/ABL1 fusion and could be considered if the results of this test are negative.

Clinical Utility

Chronic myelogenous leukemia (CML) was the first hematological disorder to be associated with a specific chromosome abnormality, the t(9;22)(q34;q11.2) which generates the Philadelphia chromosome (truncated chromosome 22). The molecular consequence of this translocation is fusion of the 3' segment of the Abelson (ABL1) proto-oncogene on chromosome 9q34 to the 5' segment of the BCR gene on chromosome 22q11.2, producing a chimeric 210 kDa BCR/ABL1 fusion gene product. At diagnosis, over 90% of CML patients will demonstrate the t(9;22)(q34;q11.2) by conventional cytogenetic analysis. The remaining cases either present a submicroscopic rearrangement or a variant t(V;9;22) translocation. In these cases, FISH analysis can readily detect the BCR/ABL1 fusion, and failure to do so would suggest that another myeloproliferative disorder, such as chronic neutrophilic leukemia, should be considered. 

This assay utilizes a dual color dual fusion (DCDF) BCR/ABL1 FISH probe that provides the highest sensitivity (approximately 98-99%) with the lowest number of false positive and false negative rates. The ABL probe extends from a region centromeric of the ASS gene, through the ABL gene, and distal to a region telomeric of the last ABL exon. The LSI BCR probe is composed of two separate genomic targets spanning a region which begins 5' of the BCR gene and ends at a point well distal to BCR, with an intervening gap in coverage of 300 kb. BCR/ABL fusion generates a double fusion (yellow or orange/green) signal pattern because both the der(9) [ABL1/BCR] and der(22) [BCR/ABL1] loci are detected. The D-FISH BCR/ABL1 probe will detect translocations occurring at the typical major breakpoint cluster region (M-BCR) that generates the p210 product, but will also identify a breakpoint in the mu region (µ-BCR) which produces a larger fusion protein (p230) rarely observed in CML as well as a breakpoint in the minor breakpoint region (m-BCR) producing the shorter fusion product (p190) most often observed in Ph+ ALL. An alternative BCR/ABL1 FISH probe (BCR/ABL1 +ASS gene) can also identify a deletion of the ASS gene which has previously been associated in some studies with a shortened chronic phase and decreased overall survival; however, the negative prognostic impact of this abnormality appears to have been mitigated by Gleevec therapy. BCR/ABL FISH analysis of peripheral blood specimens is a common practice for routinely monitoring CML patients.

CPT Codes

88271x2 DNA probe, each (BCR/ABL1 DCDF), 88271x3 DNA probe, each (BCR/ABL1 + ASS gene), 88275x1 Interphase analysis, 100-300 cells.


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