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CancerQuest > Introduction to Patient Information > Introduction to Cancer Detection and Diagnosis > Fluorescence in Situ Hybridization (FISH)

Fluorescence in Situ Hybridization (FISH)

Fluorescence in Situ Hybridization

FISH is a technique that measures gene amplification using fluorescently labeled DNA (probe). The sample of breast tumor tissue is prepared for FISH by heating it. This heating process breaks the DNA into two strands; this produces two single strands of DNA and is called denaturing. The labeled probe is added to the denatured DNA mixture. The fluorescently labeled DNA matches certain regions of the denatured DNA and when the matching regions come in contact with each other they bind. After a set period of time the mixture is washed so any unbound labeled DNA is removed. The washed mixture is viewed using a special fluorescence microscope that can detect the probe. Presence of the probe marks the areas of DNA (genes) that code for the protein of interest, thus the amount of probe present indicates the number of genes present coding for the protein. ^{(1) (2) (3)}

FISH is a fast and highly sensitive technique that provides an objective scoring system. It is more expensive than IHC and requires a fluorescence microscope for interpretation, so it is not available in all areas. ^{(1) (4) (5)}

FISH for determination of HER2 status in breast cancer

In the case of HER2 status of breast cancer, the radioactively labeled DNA probe is complimentary to a DNA region coding for the HER2 protein. Pathologists can determine the number of HER2 genes present by counting the number of probes in the sample. A tumor is considered HER2 positive if a sample has over 2 copies of the HER2 gene per chromosome 17.⁽¹⁾

A sample of an entire set of chromosomes that has been labeled with different colored dyes using a variation of the FISH technique is shown below:

References for this page:

1. DG Hicks, RR Tubbs. Assessment of the HER2 status in breast cancer by fluorescence in situ hybridization: a technical review with interpretive guidelines. Human Pathology. 2005 Mar;36(3):250-61. [PUBMED]
2. DG Hicks, RR Tubbs. Assessment of the HER2 status in breast cancer by fluorescence in situ hybridization: a technical review with interpretive guidelines. Human Pathology. 2005; 36:250-261. [PUBMED]
3. M Bilous, M Dowsett, et al. Current Perspectives on HER2 Testing: A Review of National Testing Guidelines. Modern Pathology. 2003; 16(2):173-182. [PUBMED]
4. DG Hicks, RR Tubbs. Assessment of the HER2 status in breast cancer by fluorescence in situ hybridization: a technical review with interpretive guidelines. Human Pathology. 2005; 36:250-261. [PUBMED]
5. M Bilous, M Dowsett, et al. Current Perspectives on HER2 Testing: A Review of National Testing Guidelines. Modern Pathology. 2003; 16(2):173-182. [PUBMED]