فارسی
BCR-ABL test is a genetic test used to diagnose certain blood cancers. In this test, the presence of the BCR-ABL gene sequence on chromosome 22 is examined, which helps diagnose this type of cancer.
Additionally, this test is used to monitor treatment effectiveness and diagnose cancer recurrence. BCR-ABL is actually an abnormal gene sequence that is created due to chromosomal translocation between chromosome 22 and chromosome 9, resulting in the creation of the fusion gene “BCR-ABL1”. This gene complex places the ABL1 gene from chromosome 9 next to the BCR gene from chromosome 22 due to this chromosomal translocation. The expression of this new complex gene leads to the production of a hybrid protein with tyrosine kinase activity. This hybrid protein always keeps the cell division command key in the “on” state, leading to uncontrolled cell division.
The presence of this chromosomal translocation is a sensitive test for the diagnosis of chronic myeloid leukemia (CML) of the bone marrow, as 95% of patients with this disease have this chromosomal translocation. However, it should be noted that the presence of the Philadelphia chromosome is not a specific test for the diagnosis of this disease, as it is sometimes observed in acute lymphoblastic leukemia (ALL) and occasionally in acute myeloid leukemia (AML).
In the qualitative BCR-ABL test, the presence of the BCR-ABL fusion gene on chromosome 22 is examined. To perform the qualitative BCR-ABL test, a blood or bone marrow sample is taken from the patient. Then, using various techniques, the presence of the BCR-ABL fusion gene on chromosome 22 is examined. The reported result is positive or negative. If the reported result is positive, it indicates the presence of the BCR-ABL fusion gene on chromosome 22 and the diagnosis of chronic myeloid leukemia (CML) and a type of acute lymphoblastic leukemia (ALL), and rarely acute myeloid leukemia (AML).
There are several qualitative methods for detecting the BCR-ABL gene sequence in a patient’s blood or bone marrow sample, including PCR (Polymerase Chain Reaction) and FISH (Fluorescence In Situ Hybridization). In the karyotype method, the presence of the Philadelphia chromosome BCR-ABL is examined in the blood or bone marrow sample by analyzing the chromosome. In the PCR method, specific primers for the fusion gene are used, and if the BCR-ABL gene sequence is present in the blood or bone marrow sample, the PCR product will be produced. In the FISH test, the presence of the BCR-ABL gene sequence in the blood or bone marrow sample is examined using fluorescent probes.
In the quantitative BCR-ABL test, the level of BCR-ABL in the blood or bone marrow sample is periodically requested to examine and control the response to treatment and the possibility of disease recurrence for the patient. The level of BCR-ABL is reported as a percentage of the total number of ABL gene copies in the blood or bone marrow sample. There are different methods for the quantitative BCR-ABL test. Currently, the Real-time PCR method is known as one of the most accurate and fastest methods for detecting and examining the level of BCR-ABL gene copies in peripheral blood samples of patients. To perform this test, RNA extracted from the patient’s peripheral blood is first used to make cDNA using the RT-PCR method, and then it is amplified using hybrid probes and specific DNA primers. In this test, each sample is examined for the presence of mRNA for two BCR-ABL (MBCR) and ABL genes. Therefore, two PCR tests must be performed in separate tubes. Five standards for the MBCR gene and three standards for the ABL gene are used in each PCR test along with patient samples, and the number of cDNA copies of the patient sample is determined and measured based on the ratio of the BCR-ABL gene standard curve to the ABL gene. It should be noted that to increase accuracy in each test, one sample is examined twice, and to ensure that no contamination and false positive results are created, a negative control sample is used for each of the BCR-ABL and ABL genes in each test
