BCR-ABL1 T(9:22)

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1.     What is the BCR-ABL1 fusion gene? What is its role in causing cancer?

BCR-ABL1 is a proto-oncogene with persistently enhanced tyrosine kinase activity. This kinase activity is in charge of maintaining cell proliferation, inhibiting its differentiation and giving resistance to cell death. As the result, abnormal cells keep proliferating in an uncontrolled, uninhibited fashion giving rise to cancers. Depending upon the location of break-in chromosome 22, proteins or fusion transcripts of different sizes and weights are produced. Three BCR-ABL1 fusion gene hybrids encode BCR-ABL1 protein isoforms p210, p190 and p230. Amongst these three, p210 (210-kDa protein) is most commonly detected in CML which is a major BCR-ABL1 transcript. p190 (190-kDa protein) is a minor BCR-ABL1 transcript commonly found in B-cell ALL and occasionally in AML. The molecular diagnostic hallmark of neutrophilic CML is p230, a 230-kDa protein.

2.     What is leukemia?

Leukemias are the cancer of blood-forming cells. Blood cells are constituents of blood which includes red blood cells, white blood cells and platelets. Their precursors are present in bone marrow in an immature form and from these marrow stem cells, blood constituents get matured for functioning.

3.     What are the initial signs and symptoms of CML?

Usually, initial symptoms are non-specific and may get depicted on peripheral blood (CBC) report. Symptoms include fever, weight loss, loss of appetite, weakness, fatigue, joint or bone pain, night sweats, abdominal pain and liver or spleen swelling (massive splenomegaly). As disease advances, patients have symptoms of anemia, recurrent infections and prolonged bleeding.

4.     What are the phases of CML?

CML disease progression involves these 3 stages:

i. Chronic phase - Most people with CML are diagnosed in this phase. It is usually insidious in onset, meaning that leukemia symptoms may be absent or subtle. Patients have less than 10% immature blood cells or blasts in blood or bone marrow. A chronic phase may last for few months to several years. This is the period when treatment is most successful.

ii. Accelerated phase - In this phase, changes include increasing WBC counts, despite giving treatment or when unresponsive to therapy, additional changes like increase in blast cells (10-19% blasts), or additional chromosome abnormalities besides Ph chromosome.

iii. Blast phase - When blasts are 20% or more in the blood or bone marrow or when there is blast proliferation outside the marrow.

5.     What percentage of CML and ALL cases are Ph chromosome-positive at diagnosis?

At diagnosis, approximately 90-95% of cases of CML are positive for t(9;22). About 30% of adults and only 2-4% of children with B-ALL show this translocation.

6.     If I am positive for the Ph chromosome, should my family members get tested?

No. This is not an inherited genetic abnormality.

7.     Can I directly ask for this testing if I have symptoms?

No. It is always the treating physician’s call. After correlating with other lab parameters, symptoms and clinical findings, the decision of doing BCR-ABL1 testing is taken based upon suspicion of having CML or ALL. 

8.     Is there any other test done in patients with BCR-ABL1 translocation?

Yes. Real-time PCR-Polymerase chain reaction, cytogenetic studies (chromosomal karyotyping) and DNA sequencing techniques are useful for detecting BCR-ABL1. PCR can be qualitative or quantitative, and it can detect even very small amounts of BCR-ABL1. In quantitative real-time PCR, we get results in copy number/ml of the BCR-ABL1 transcripts. This gives us the baseline values of copy number which helps in monitoring response to therapy, see for remission and disease recurrence. FISH is preferred over conventional cytogenetic testing because results are more quickly available.

9.     Does this testing impact cancer treatment?

Yes. If a patient is positive for the Ph chromosome, tyrosine kinase inhibitors can be used for treatment as these patients have enzyme tyrosine kinase-mediated uncontrolled growth of leukemic cells.

10.   What should be done if a patient is resistant to treatment?

If a person is not responding to treatment, there is suspicion of treatment resistance or disease recurrence; you need to test for BCR-ABL1 kinase domain mutation analysis.

11.   Do I need to repeat this test?

Yes. Your clinician may order repeat tests to look for additional mutations or genetic abnormalities which can be acquired as time passes by and the disease progresses.

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