Fluorescent Situ Hybridization FISH DNA Test

What is a Fluorescent in situ hybridization FISH DNA test?

Fluorescence In-Situ Hybridization is a method used to identify specific parts of a chromosome. FISH can be used to detect small deletions and duplications that are not visible using microscope analysis like karyotyping. It can also be used to detect how many chromosomes of a certain type are present in each cell and to confirm rearrangements that are suspected after microscope analysis.

Your body contains all of the information to function within DNA molecules strung along the 46 chromosomes found in normal cells. Cancer cells, which behave in an abnormal way and grow out of control, may have noticeable changes in those chromosomes, including:

• Duplication. There may be extra copies of a portion of a chromosome, also called amplification.
• Deletion. There may be a portion missing.
• Inversion. A portion may be reversed.
• Translocation. A portion may have moved to another chromosome.

How does FISH work?

FISH is useful, for example, to help a researcher or clinician identify where a particular gene falls within an individual's chromosomes. The first step is to prepare short sequences of single-stranded DNA that match a portion of the gene the researcher is looking for. These are called probes.

The next step is to label these probes by attaching one of a number of colours of fluorescent dye.DNA is composed of two strands of complementary molecules that bind to each other like chemical magnets. Since the researchers' probes are single-stranded, they are able to bind to the complementary strand of DNA, wherever it may reside on a person's chromosomes. When a probe binds to a chromosome, its fluorescent tag provides a way for researchers to see its location.

What is the cost of FISH?

The cost of the FISH Test ranges from Rs.6000 to Rs.22000

Why has FISH been recommended?

FISH is often performed alongside standard microscope analysis if the patient has characteristics that are strongly suggestive of a particular deletion syndrome or another syndrome for which a FISH test is available. Your Physician may request microscope analysis and FISH testing together or may request FISH testing if microscope analysis gives a normal result. 

Your doctor can use more than one method to check your HER2 levels. If your results weren't clear with the first test, your doctor may also do or repeat a FISH test to double-check them. Your HER2 levels may change if your cancer comes back after treatment or spreads beyond the breast tissue. If this happens, your doctor may do a FISH test to understand which treatments will now work best for you.

What samples are needed for FISH testing?

FISH is most commonly performed on blood samples from adults and children. FISH can also be used as a prenatal test for aneuploidy (extra copies of whole chromosomes) using amniotic fluid from amniocentesis or placental samples from chorionic villus sampling (CVS). Less commonly it is used as a prenatal test for deletions, also using amniotic fluid or CVS samples.

What the Results Mean

FISH testing usually returns one of two results: 

• Positive means your breast cancer cells make too much HER2 and your doctor should treat you with drugs that target that protein.
• Negative means the protein isn't involved in the growth of your tumour. If you get this result, your doctor will choose a different treatment plan.
• Sometimes FISH test results are unclear. If this happens, your doctor may do more tests to try to get a clear answer about your HER2 protein levels.