What is FISH Test & How Does it Help in Cancer Detection?

One of the most feared, complex and fatal diseases that has become the cause of death for many is cancer. Cancer is a disease in which cells and tumours become malignant and spread in an unhealthy way. Cancer can occur in almost any and every part of the body. Although early determination and diagnosis of cancer can cure or at least treat the disease; however, most of the times, in the early stage it becomes difficult to diagnose Cancer, since the symptoms are not pronounced. In fact tests also do not confirm the presence of malignant/cancer cells in the body easily.¹ However, one test that is common and widely used in determining cancer is FISH test.

FISH test or Fluorescence In-Situ Hybridization is a test used to detect cancer by ‘mapping’ the genetic materials present in human cells. To be more specific, FISH test is a branch of genetics that mainly detects and tries to locate the presence as well as absence of specific or particular sequences of DNA in chromosomes. This test is also known as Molecular Cytogenetics.

With this test, genetic abnormalities that are linked with diseases like cancer can be detected. The best application of FISH test is to determine the type of the cancer. In those cases, where the type of cancer has already been detected by some other test, the FISH test helps to determine whether a patient is able to take chemotherapy drugs and respond to this cancer treatment. Additional information is also required by the doctor to determine the patient’s condition and outcome from cancer; whether he or she is responding to cancer treatment or not, FISH test also helps to detect this additional information. In most cases, this FISH test is done to detect breast cancer, by collecting tissue from the breast tumours during biopsy or other surgeries.

The FISH test can detect, if the breast cancer cells containing extra genes and DNA are.

• Producing some particular proteins.
• Prohibiting the cells to make the protein.
• Making protein in large amounts than normal.²

Since FISH test is done to determine breast cancer in most of the cases, the mechanism of breast cells needs to be understood first. The breast cell contains HER2 gene in its chromosomes. The HER2 or Human Epidermal Growth Factor Receptor 2 is a receptor protein. The HER2 gene in a normal breast cell will instruct the cell to produce HER2 protein in proper amount. The HER2 receptor or protein gives the cell the instruction and sends signals telling the cell to grow itself and divide into more cells. When there are extra copies of the HER2 gene in the breast cell, the HER2-positive breast cells are deemed as cancer cells causing the cells to grow and divide more quickly.³

During the test, samples of the cancer tissue are collected at first. They are then spread on slides to check if the cells have extra copies of HER2 genes. Those cells that have extra copies of the HER2 genes will have more HER2 receptors or produce more HER2 protein and are considered to be cancerous.

A special coloured dye is used to colour some parts of the specific chromosomes for determining its type. This helps the pathologist to count the chromosomes with proper visualizing opportunity, when the sample with the coloured dye attachment is placed under a fluorescent microscope. The dye works as a specific marker that will indicate any change in the DNA or the parts of the chromosomes and also help the pathologist to count the chromosome or genes, thereby determining the extra presence of these genes within the cancerous cells.

As the genetic markers or the fluorescent dye sticks to the genes, it clearly shines when the cells are placed under ultraviolet light in the fluorescent microscope. When the pathologist looks into the microscope, the dyed region is clearly shown as a brightly glowing area.⁴

In case of breast cancer cells that are mostly determined by the FISH test, the fluorescent dye will clearly show that the HER2 gene as a more glowing region, since they are more in number than normal. However, in general and in all other cancer detections, the abnormalities that FISH test can find are.

• Inversion. If some parts of the chromosome lies in a reverse order, despite being attached to the proper chromosome.
• Translocation. When some parts of the chromosome gets broken and gets relocated to another chromosome.
• Duplication. When parts of the chromosome are copied and there are too many duplicates in the cell.
• Deletion. When parts of the chromosome gets deleted.

The other diseases that can also be detected with the help of FISH test or Fluorescence In-Situ Hybridization test are lymphoma, leukemia and also sarcoma. All these diseases are associated with the abnormality of the chromosome where parts of the chromosome get translocated.⁵

FISH Test Detects Minute Cell Changes. Since the genetic changes are very crucial to be identified by the pathologist in order to determine and detect the cancer cells,

FISH test or Fluorescence In-Situ Hybridization test is the best way to do this. This is because no other test can display the small genetic changes under the microscope like this one.

FISH Test Confirms Cancer In Its Initial Stages. As most of the cancer cells take about two weeks to grow and divide, when the sample is collected at the lab dish, the pathologist has to wait for weeks to let the sample cells grow and divide, in order to run the test. However, in FISH test, the active cell division is not required. Only the presence of these cell dividing extra copies of HER2 genes can detect the malignancy of these cells. Hence, the results can be determined within a few days.⁶

FISH test is quite an expensive test and is not widely popular, despite its accuracy and potential to detect some kinds of cancers. Moreover, it is still not known whether FISH test will be useful in determining and detecting all kinds of cancers or not. This is because the genes that should be looked for in order to perform the FISH test for different cancer cells are not yet known. Chronic lymphocytic leukaemia and breast cancer are the two common cancers that are best determined by FISH test. Lung cancer and stomach cancer are also being determined by FISH test.

The FISH or Fluorescence In Situ Hybridization test is a highly potential test for determining some cancers and other similar gene abnormality related diseases. The test is likely to be done and used more widely in the times to come.

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