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FISH testing

Get information about what FISH testing is and how it is done.

FISH stands for fluorescence in situ hybridisation. It is a test that looks for gene changes in cells. Genes are made of DNA. They control everything the cell does, including when it grows and reproduces. FISH tests look for specific genes or parts of genes.

Changes in cancer cell genes can make the cell:

  • produce particular proteins
  • make far more of the protein than normal
  • stop making a particular protein

Some proteins help to control the cell, telling it to grow or reproduce more often.

If a gene change occurs, the cell may produce too much of a protein or not enough. This can make the cancer cells grow and reproduce more than normal. In cancer treatment doctors use the FISH test to look at the genetic make up of your cancer, not at your normal cells.

Cancer treatment

There are now cancer treatments that target specific proteins. Finding out if your cancer has a particular change in its genetic make up can help your doctor to know whether a particular treatment is likely to work for you.

Some breast cancers produce too much of the protein HER2 because of a change in a gene called HER2/neu. Doctors might do a FISH test to measure the amount of HER2/neu gene in each cancer cell.

If the FISH test comes back strongly positive for HER2, it is much more likely that a drug called trastuzumab (Herceptin) will work. Trastuzumab targets the HER2 protein.

How is FISH testing done?

FISH testing is done by a pathologist. A pathologist is an expert who examines and identifies cells.

To do a FISH test the pathologist needs some tissue from your cancer. This can be from a biopsy or from when you had surgery to remove your cancer. In the laboratory the pathologist attaches a dye to specific markers for the gene change they are looking for. They then put the markers on the cancer cells from your biopsy or surgery.

The genetic markers stick to the particular gene that the marker targets. The pathologist shines an ultraviolet light on the cells. Under the microscope the gene shows up as a bright glowing area.

How available is FISH testing?

At the moment FISH tests are only used for a few cancers including breast cancer and chronic lymphocytic leukaemia.

They are also being tested in stomach cancer and lung cancer. We don’t yet know enough about which genes to look for to be able to develop FISH tests for other cancers.

Doctors and researchers are finding out more each day about genetic changes that affect how cancers grow. So, in the future FISH tests should become available for more cancer types.

Last reviewed: 
17 Apr 2013
  • Fluorescence In Situ Hybridization (FISH) Fact Sheet

    National Human Genome Research Institute, 2013

  • Gastric HER2 Testing Study (GaTHER): an evaluation of gastric/gastroesophageal junction cancer testing accuracy in Australia

    SB Fox and others

    American Journal of Surgical Pathology, 2012

    Volume 36, Issue 4

  • Textbook of Medical Oncology (Fourth Edition)

    F Cavalli and others

    CRC Press, 2009

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