FISH Testing: How It Identifies Hidden Cancer Cells

FISH (Fluorescence in situ hybridisation) test is a laboratory test that can confirm the HER2 status of breast cancer. Tissue from a biopsy or breast cancer surgery is used for the test. A fluorescent dye is used in a FISH test to identify more copies of the HER2 gene in breast cancer. This article explains about the FISH testing and how it identifies the hidden cancer cells.  

What is the FISH test?

In genetic testing, pathologists employ fluorescence in situ hybridisation to aid in the diagnosis of disease brought on by chromosomal abnormalities. FISH can also be used by medical professionals to identify gene alterations that they can target in cancer treatment. FISH paints portions of chromosomes or genes that pathologists search for in order to diagnose illness using proteins or chemical markers. When viewed under a microscope, the labels appear as colourful lights.  

The information in the genes that instructs your body how to function is found in your DNA. Chromosomes are structures that resemble threads and are used to organise genes. Your cells may receive incorrect instructions if there are errors in your instruction manual, such as words that are removed, repeated or rearranged. Information contained in single genes or entire chromosomes may be absent, duplicated or relocated. These variations may result in diseases like cancer or alter the way your body functions.  

What can FISH be used to test for?

FISH is an abbreviation for florescence in situ hybridisation. It is most commonly used for:

• Large-scale gene mutation in cancer
• To find the chromosomal abnormalities before or after birth
• Chromosomal abnormalities in an embryo during preimplantation genetic testing as a part of IVF

FISH test procedure

The FISH test procedure involves various steps:

In order to observe and count certain chromosomes under a fluorescence microscope and identify defects that promote cancer, special-coloured dyes are added to specific sections of the chromosomes during a FISH test.  

In the FISH technique procedure, the abnormalities found in cancer cells include,  

• Translocation: It is a part of one chromosome which has broken off and relocated itself onto another chromosome.
• Inversion: It is a part of a chromosome which is in reverse order, although it is still attached to the correct chromosome.  
• Deletion: It is a part of a chromosome that is missing.
• Duplication: A part of a chromosome that has been copied, and the cell contains too many copies.

Certain forms of leukaemia, lymphomas and sarcoma can be identified by physicians with the aid of translocations. Breast cancer cell duplications can aid medical professionals in selecting the best course of action.  

One benefit of FISH over conventional cytogenetic testing is its ability to detect genetic alterations that are too minute to be visible under a microscope. A further benefit is that cells that are actively dividing do not need to be used for FISH. The processes typically take around three weeks since other tests cannot be conducted until the cancer cells have been growing in lab dishes for approximately two weeks. Results from FISH are typically available in a few days.  

FISH test for cancer

The FISH test for cancer can reveal crucial details about numerous other cancer forms, even though it is frequently used to examine genetic abnormalities in breast cancer. For instance, FISH testing of urine cells may be more accurate than a typical test that searches for aberrant cells in the detection of bladder cancer. Furthermore, bladder cancer recurrences may be detected three to six months sooner with FISH.  

Chromosome abnormalities in leukaemia, such as chronic lymphocytic leukaemia cells, which are sometimes linked to aggressive versions of the illness, can also be detected by FISH. While patients with less aggressive forms of CLL might only need observation, those with more aggressive forms might require immediate treatment.  

Gene changes detected by FISH

The pathologists employ FISH to analyse the tumour cells obtained from the biopsied tissues of the patient for any genetic alterations or mutations, which could possibly lead to specific cancers or any other diseases. Specific changes that FISH can detect include:

• Amplifications: Amplification refers to an increase in the number of genes. These usually happen in cases where the cancer genes are overly expressed in the tumour cells. This would indicate the prognosis of the disease and can give better clarity when deciding the therapy for the patient.
• Translocations/rearrangement: Rearrangements are commonly seen in the majority of cancers, including breast cancer, where a genetic component has displaced from its original position to some other position, causing chaos in protein synthesis. These kinds may result in altered protein synthesis, which could aid in cancer growth.  
• Deletions: Some probes might stick to a section of the DNA in the sample, and others might not stick where they should. If the DNA isn’t labelled where it should be, some information is missing (deletion).

FISH test for breast cancer

The HER2 status of breast cancer is determined via a FISH test. In breast cancer cells, it counts the quantity of HER2 genes. An excessive number of HER2 gene copies causes a breast cancer cell to produce more HER2 proteins than usual. These proteins serve as receptors on breast cancer cells, receiving signals that promote the disease’s growth.  

HER2-positive breast cancer is defined as having an excess of HER2 receptors. Your doctor decides on a course of treatment based on whether the breast cancer is HER2-positive or HER2-negative. If the results of the initial HER2 status test, the IHC test, are not conclusive, a FISH test for breast cancer is typically performed. Not all breast cancers need FISH testing.  

A positive result indicates that the cancer is HER2-positive, while a negative or zero result indicates that the cancer is HER2-negative. Many breast cancers that are classified as HER2-negative have some HER2 proteins on the surface of their cells. Doctors refer to these cancers as HER2-low. Targeted therapies are available to treat both HER2-positive and HER2-low breast cancer.  

Conclusion  

In conclusion, FISH is a confirmatory test for breast cancer. The biopsy that is taken during the surgery is treated with fluorescence dye to identify the types of genes in the tumour cells. Medical innovations have led to the expansion of this test into broader cancers such as haematological cancers and many more. It helps a medical oncologist to decide the regimen and treat it with the aim of complete remission.