Breast cancer is one of the most common cancers among women. As of 2022, it caused 6.7 lakh deaths globally. According to the World Health Organization (WHO), roughly half of all breast cancers occur in women with no specific risk factors other than sex and age. In rare cases, men too can develop breast cancer.
Early diagnosis of breast cancer is key, as it allows for timely treatment and improves outcomes. Common screening methods include self-breast examinations, mammograms, breast ultrasounds, breast magnetic resonance imaging (MRI), and biopsies. Another valuable tool in breast cancer detection is fluorescence in situ hybridisation (FISH) testing.
Speaking with the OnlyMyHealth team, Dr Ajay Shah, Managing Director of Neuberg Ajay Shah Laboratory, explains the role of the FISH test, its functioning, and its limitations.
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What Is FISH Testing For Breast Cancer?![]()
Dr Shah describes FISH testing as a molecular diagnostic technique used to detect specific genetic abnormalities within breast cancer cells.
"It works by using fluorescent probes that bind to certain DNA sequences, allowing for the visualisation of gene amplifications or deletions under a microscope," he explains.
Talking about its role in breast cancer detection, he further states that the FISH test is primarily used to evaluate the HER2 gene (human epidermal growth factor receptor 2) status. If there are too many copies of the HER2 gene, the cancer is classified as HER2-positive, indicating a more aggressive form of cancer that may respond well to targeted therapies.
What Is HER2-Positive Breast Cancer?![]()
HER2-positive breast cancer is a type of breast cancer that has high levels of the human epidermal growth factor receptor 2 (HER2) protein, which controls cell growth and division.
According to the American Cancer Society (ACS), HER2-positive breast cancer tends to grow and spread faster than other types of breast cancer.
Dr Shah explains, “In normal cells, there are two copies of the HER2 gene, but in HER2-positive breast cancer, the gene is amplified, leading to overproduction of the HER2 protein. This overexpression promotes cancer cell growth and spread.”
How Accurate Is FISH Testing In Breast Cancer Diagnosis?
According to a 2012 study published in Modern Pathology, FISH testing is the gold standard for diagnosing HER2 status in breast cancer.
Dr Shah says that this type of testing is preferred in some breast cancer cases due to its high accuracy and reliability in detecting HER2 gene amplification.
"While other methods, such as immunohistochemistry (IHC), assess HER2 protein expression levels, they can sometimes give ambiguous results. FISH offers a more definitive answer by directly measuring gene amplification, which is essential for making precise treatment decisions. In cases where IHC results are inconclusive or borderline, FISH is used as a confirmatory test to ensure accurate diagnosis," the doctor adds.
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How FISH Testing Influences Treatment Plan For Breast Cancer![]()
According to Dr Shah, “FISH testing plays a critical role in shaping the treatment plan for breast cancer patients, particularly those with HER2-positive cancer. If FISH results show HER2 gene amplification, the patient is classified as HER2-positive, indicating that targeted therapies, such as trastuzumab (Herceptin) or pertuzumab (Perjeta), could be highly effective. These drugs specifically inhibit the growth-promoting effects of the HER2 protein, improving treatment outcomes and survival rates. On the other hand, if the FISH test shows no HER2 amplification (HER2-negative), these targeted therapies would not be effective, and the patient may instead receive other forms of treatment such as hormone therapy or chemotherapy. Thus, FISH testing helps doctors tailor a more precise and personalised treatment plan.”
Limitations Of FISH Testing
Just like any other screening methods or tools, FISH testing, while highly accurate, comes with some limitations and challenges.
One of the main challenges is its cost, as it can be more expensive than other testing methods like immunohistochemistry (IHC). Additionally, FISH testing requires specialised laboratory equipment and expertise, making it less accessible in some healthcare settings.
Interpretation of FISH results can also be complex, especially when the gene amplification is low or borderline. There are also technical difficulties related to sample preparation, such as tissue quality, that can affect the accuracy of the test. Finally, FISH is specific to detecting HER2 gene amplification, so it doesn’t provide information on other genetic mutations or markers that may influence breast cancer treatment.