Pathology dictionary

Fluorescence in situ hybridization (FISH)

What is fluorescence in situ hybridization (FISH)?

Each cell in your body contains a set of instructions that tell the cell how to behave. These instructions are written in a language called DNA and the instructions are stored on 46 chromosomes in each cell. Because the instructions are very long, they are broken up into sections called genes and each gene tells the cell how to produce piece of the machine called a protein.

Some tumours contain changes that alter the location or amount of DNA in a predictable manner. Pathologists use their knowledge of these changes to identify specific types of tumours.

Fluorescence in situ hybridization (FISH) is a test pathologists perform to learn more about the genetic material in a cell. FISH uses a fluorescent probe which has been designed to stick to a unique segment of DNA (the target). FISH probes are called fluorescent because they only produce a colour when they are exposed to certain types of light. As a result, pathologists need to use a special type of microscope which can produce specific types of light and detect the colour coming from the probe.

The results are captured in an image on a computer for further analysis. When the probe finds a change in the location of the target DNA, the result is called a translocation. When the probe finds a change in the total amount of target DNA, the result is called an amplification or deletion depending on the type of change identified.​

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