An atypical and complex BCR-ABL translocation in a chronic myeloid leukemia patient and its response to TKI therapy
Cancer Genetics and Therapeutics
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Primary Categories:
- Cancer
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Secondary Categories:
- Cancer
Introduction:
Philadelphia (Ph) chromosome is found in around 90-95% of Chronic Myeloid Leukemia (CML) patients. This genetic abnormality is known as a balanced chromosomal translocation, t(9;22), involving the fusion of the breakpoint cluster region (BCR) gene of chromosome 22 with the Abelson (ABL) gene from chromosome 9, resulting in an oncogenic BCR-ABL fusion gene product with constitutive activation of tyrosine kinase activity, which leads to uncontrolled cell proliferation. The Ph chromosome refers to the altered chromosome 22 with the ABL joins to BCR in which the abnormally activated kinase resides. The understanding of this BCR-ABL translocation has not only been instrumental in comprehending the molecular basis of CML, but has also paved the way for the development of targeted therapies.
The quantitative RT-PCR method (qRT-PCR) is often used to determine the presence of BCR-ABL translocation in. We present a case study where the initial p190 and p210 qRT-PCR results were positive, confirming the presence of BCR-ABL fusion. However, a month later, before the treatment began the qRT-PCR test results showed negative. Additional genetic testing was ordered for this patient to either rule out the possibility of false testing results or determine whether the abnormality has evolved into an atypical BCR-ABL translocation.
Methods:
The BCR-ABL fusion proteins of molecular mass 190 (p190) and 210 (p210) were tested using qRT-PCR in the patient’s bone marrow specimens in July and August 2024. For chromosome karyotyping, ten metaphase cells were analyzed from the culture supplemented with GM-CSF and ten metaphase cells were analyzed from the 24-hour unstimulated culture. A mixture of three apparently normal cells and seventeen abnormal cells were observed. In addition, both metaphase and interphase fluorescence in situ hybridization (FISH) tests were performed with LSI BCR probe labeled green and LSI ABL probe labeled red to visualize the Ph chromosome and determine the percentage of abnormal cells.
Results:
The qRT-PCR in July and August 2024 showed positive and negative test results, respectively. The chromosome karyotyping gave an abnormal clone in the patient specimen with the nomenclature as 46,XY,t(1;9;22;12)(q32;q34;q11.2;p13)[17]/46,XY[3]. The interphase FISH showed an atypical pattern of one fusion, two red, and two green signals with 75% abnormal cells. The metaphase FISH showed der(9), der(12), and der(22) chromosomes.
Conclusion:
The chromosome karyotyping and FISH results are concordant, all indicate the presence of Ph chromosome in the patient. The abnormality detected in the July 2024 qRT-PCR was not detected in the August 2024 analysis, which is likely attributable to the presence of a cryptic BCR-ABL rearrangement. The TKI treatment of the cryptic BCR-ABL translocation is ongoing and the response will be discussed.
Philadelphia (Ph) chromosome is found in around 90-95% of Chronic Myeloid Leukemia (CML) patients. This genetic abnormality is known as a balanced chromosomal translocation, t(9;22), involving the fusion of the breakpoint cluster region (BCR) gene of chromosome 22 with the Abelson (ABL) gene from chromosome 9, resulting in an oncogenic BCR-ABL fusion gene product with constitutive activation of tyrosine kinase activity, which leads to uncontrolled cell proliferation. The Ph chromosome refers to the altered chromosome 22 with the ABL joins to BCR in which the abnormally activated kinase resides. The understanding of this BCR-ABL translocation has not only been instrumental in comprehending the molecular basis of CML, but has also paved the way for the development of targeted therapies.
The quantitative RT-PCR method (qRT-PCR) is often used to determine the presence of BCR-ABL translocation in. We present a case study where the initial p190 and p210 qRT-PCR results were positive, confirming the presence of BCR-ABL fusion. However, a month later, before the treatment began the qRT-PCR test results showed negative. Additional genetic testing was ordered for this patient to either rule out the possibility of false testing results or determine whether the abnormality has evolved into an atypical BCR-ABL translocation.
Methods:
The BCR-ABL fusion proteins of molecular mass 190 (p190) and 210 (p210) were tested using qRT-PCR in the patient’s bone marrow specimens in July and August 2024. For chromosome karyotyping, ten metaphase cells were analyzed from the culture supplemented with GM-CSF and ten metaphase cells were analyzed from the 24-hour unstimulated culture. A mixture of three apparently normal cells and seventeen abnormal cells were observed. In addition, both metaphase and interphase fluorescence in situ hybridization (FISH) tests were performed with LSI BCR probe labeled green and LSI ABL probe labeled red to visualize the Ph chromosome and determine the percentage of abnormal cells.
Results:
The qRT-PCR in July and August 2024 showed positive and negative test results, respectively. The chromosome karyotyping gave an abnormal clone in the patient specimen with the nomenclature as 46,XY,t(1;9;22;12)(q32;q34;q11.2;p13)[17]/46,XY[3]. The interphase FISH showed an atypical pattern of one fusion, two red, and two green signals with 75% abnormal cells. The metaphase FISH showed der(9), der(12), and der(22) chromosomes.
Conclusion:
The chromosome karyotyping and FISH results are concordant, all indicate the presence of Ph chromosome in the patient. The abnormality detected in the July 2024 qRT-PCR was not detected in the August 2024 analysis, which is likely attributable to the presence of a cryptic BCR-ABL rearrangement. The TKI treatment of the cryptic BCR-ABL translocation is ongoing and the response will be discussed.