The reciprocal translocation of the abl (Abelson murine leukemia) proto-oncogene on chromosome 9 to the bcr (breakpoint cluster region) gene on chromosome 22 creates a transcriptionally active, chimeric bcr-abl gene and gives rise to the Philadelphia chromosome. This gene encodes a 190- or 210-kd protein product, which is an active, deregulated, intracellular tyrosine kinase. By this mechanism, the fusion protein is thought to induce malignant transformation of hematopoietic stem cells. BCR-ABL refers to a gene sequence found in an abnormal chromosome 22 of some people with certain forms of leukemia. Humans normally have 23 pairs of chromosomes, including 22 pairs of non-sex-determining chromosomes (also known as autosomes) and 1 pair of sex chromosomes (XX for females, XY for males). Chromosomes contain a person's inherited genetic information.

The BCR-ABL gene sequence is one such acquired change that is formed when pieces of chromosome 9 and chromosome 22 break off and switch places. When this occurs, the ABL region in chromosome 9 fuses with the BCR gene region in chromosome 22. This is referred to as reciprocal translocation and this particular one is commonly expressed as t (9;22). A derivative chromosome 22 that has the BCR-ABL gene sequence is known as the Philadelphia (Ph) chromosome. It is strongly associated with chronic myelogenous leukemia (CML) and, to a lesser extent, with acute lymphoblastic leukemia (ALL). At diagnosis, 90-95% of cases of CML show a characteristic t (9;22) BCR-ABL reciprocal chromosomal translocation. These BCR-ABL gene sequences at the fusion site encode an abnormal protein. The abnormal BCR-ABL protein is a tyrosine kinase enzyme that is responsible for the development of CML and a type of ALL. It is the cause of uncontrolled growth of leukemic cells. When large numbers of abnormal leukemic cells start to crowd out the normal blood cell precursors in the bone marrow, signs and symptoms of leukemia start to emerge. Treatment of these leukemias typically involves a tyrosine kinase inhibitor (TKI).Testing for BCR-ABL detects the Ph chromosome (the derivative chromosome 22) and BCR-ABL fusion gene or its transcripts, the RNA copies made by the cell from the abnormal stretches of DNA. The presence of the BCR-ABL abnormality confirms the clinical diagnosis in CML and a type of ALL. BCR-ABL testing is ordered to detect the Philadelphia (Ph) chromosome and BCR-ABL gene sequence. It is used to help diagnose chronic myelogenous leukemia (CML) and a type of acute lymphocytic leukemia (ALL) in which the BCR-ABL gene sequence is present (BCR-ABL positive), to monitor response to treatment, and to monitor for disease recurrence. A chromosome analysis, the qualitative BCR-ABL molecular genetic test, and/or FISH may be ordered to help establish the initial diagnosis of CML or Ph-positive ALL. It is often performed along with other tests if a doctor suspects that a patient has leukemia and is trying to diagnose or rule out CML and Ph-positive ALL. The chromosomal analysis and FISH can also help to determine what percentage of patient's blood or bone marrow cells are affected. The qualitative BCR-ABL test can also help determine the breakpoint variant of BCR-ABL that is being produced. The size and weight of the BCR-ABL protein produced depends upon where the break in chromosome 22 occurred. In CML, the breakpoint in BCR is almost always in the major breakpoint cluster region (M-BCR), leading to the production of BCR-ABL protein of a larger size (p210). Breaks in the minor breakpoint cluster region (m-BCR) leads to a shorter fusion protein (p190), which is most frequently associated with Ph-positive ALL. Knowing whether a patient has a break in the major or minor BCR is important because the quantitative BCR-ABL molecular genetic test may be set up to measure a specific variant, p210 or p190, but not both.

The quantitative BCR-ABL molecular test is ordered once the BCR-ABL gene sequence has been detected and the breakpoint variant established. It may be ordered at the time of the initial diagnosis to establish a baseline value and then used periodically to monitor the person's response to treatment and, if the person achieves remission, to monitor for recurrence.

Taqman Real time PCR assay.

Every day.

3-4 days.

Bone marrow, Blood, Collect in: Lavender (EDTA), pink (K2EDTA). Stability collection to initiation of testing On Cells: Ambient: 4 hours; Refrigerated: 48 hours; Frozen at -20°C: 72 hours; Frozen at -70°C: 4 months. Do not thaw avoid repeated freezing and thawing.

NOTE: A blood sample drawn from a vein in your arm or a bone marrow sample collected using a bone marrow aspiration and/or biopsy procedure.

Separate serum or plasma from cells within 24 hours.

Frozen-20°C. Refrigerate specimen's at 2°C-4°C.

Heparinized specimens, Hemolysis sample, Quantity not sufficient for analysis, specimen grossly contaminated, specimen too old, frozen whole blood specimen, specimen leaky or tube broken.

Specific amplification curve for BCR ABL GENE indicate presence of BCR ABL in given sample. Whereas no amplification of the reference gene ABL indicates PCR inhibition. An additional amplification of the ABL gene is performed as a control for sample RNA quality and as a reference for relative quantification. For follow-up and monitoring the effectiveness of treatment, a previous stored sample, if available, will be analyzed along with the current sample to assess quantitative changes with time. This test can detect and Differentiate BCR ABL gene over the range 80-10⁹ copies/mL. However this does not mean that lower copies or higher copies cannot be detected. The lower copies can be detected in some cases. This is a limitation of the currently available extraction systems. A negative result does not preclude the presence of BCR/ABL Gene infection because results depend on adequate/proper patient sample storage and transportation as RNA is fragile and thermo labile, absence of inhibitors and sufficient RNA to be detected. Knowing whether a patient has a break in the major or minor BCR is important because the quantitative BCR-ABL molecular genetic test may be set up to measure a specific variant, p210 or p190, but not both.

The result of this test must always be correlated with clinical status and history of the patient and other relevant data and should not be used alone for the interpretation.