Are you afraid of the FISH test? Let's learn about this genetic test (Fluorescence in Situ Hybridization - FISH Test) in simple terms.

Has your doctor told you or someone in your family to have a 'FISH test'? Did you feel a little scared or nervous when you heard that name? Did you think, "What kind of strange test is this?"? It's very normal to feel that way. But there's no reason to worry. It's not as complicated as you think, and it's not something to be afraid of. Today, let's talk about what this FISH test is, what it looks for, and how it's done, very simply, in our language.

First of all, what is this FISH test?

Simply put, FISH is a specialized laboratory test that looks for changes or errors in the genes and chromosomes inside our body's cells. It's like examining our body's genetic map.

To understand this a little better, let's imagine our body as a big library.

• Chromosomes: Chromosomes are like the bookshelves in that library. Every human cell has 23 pairs of these bookshelves.
• Genes: Those books on the shelves are genes. These books contain all the instructions that our bodies need to function. Not only our hair color, eye color, height, but every function in our body is controlled by the information in these books called genes.
• DNA: The letters and words written in these books are DNA. That is, the complete set of instructions that our body needs is contained in DNA.

Now imagine that some of the books (genes) in this library have pages missing (deletion), some have been added (amplification), or a book that should be on one shelf has been moved to another shelf (translocation). What would happen if that happened? The instructions the body receives would be wrong. It is because of such wrong instructions that diseases like cancer and other genetic diseases arise.

How does this FISH test work?

Although the methodology is a bit scientific, I will explain it to you with a very simple example.

Imagine you need to find a specific sentence in a big book. What do you do? You find the sentence and mark it with a colored highlighter. Then it's easy to find it again.

This is what happens in a FISH test. In the lab, scientists make pieces of DNA that match the specific part of the gene they want to look for in your cell sample. These are called 'probes.' Then, they attach fluorescent labels to these made DNA pieces. These are like highlighter pens.

Next, they take a sample of your cells (such as blood or tissue) and add these colored labeled 'probes' to it. Then something amazing happens. The 'probe' finds the exact location of the gene that matches it and hybridizes to it.

Then, when a pathologist looks at it with a special microscope (fluorescent microscope), the 'probes' attached to that gene segment glow like colored lights, like stars shining in the dark.

• In a normal cell: The expected amount of color light is visible in the correct places.
• In an abnormal cell: You may see more colors than expected (amplification), or you may not see a color that you want to see (deletion), or you may see two colors that should be together but are far apart (translocation).

It's by looking at that glowing light pattern that doctors can tell you exactly what changes are in your genes.

What are the main things that the FISH test looks for?

The FISH test is mainly performed for several reasons. Let's take a look at the genetic changes it can detect and the diseases associated with them.

What diseases can be identified through these changes?

The FISH test is very important for diagnosing various diseases, especially cancers, and planning treatment.

• Types of cancer:
• Breast Cancer: Specifically, look for amplification of the gene (HER2). If there is such an amplification, specific treatments can be given that are specifically targeted to that gene.
• Leukemia: Identify the types of acute and chronic leukemia.
• Lymphoma
• Bone marrow cancer (Multiple Myeloma)
• Lung, stomach, and bladder cancers
• Prenatal and postnatal genetic conditions: Test a baby before or after birth to see if they have chromosomal abnormalities, such as Down syndrome.
• In vitro fertilization (IVF): This method is also used to test embryos for chromosomal abnormalities before they are transferred through in vitro fertilization (IVF).

How should I prepare for the FISH test?

How you prepare for this test depends on the sample you are taking. There are different types of samples that can be taken for this purpose.

• Blood Test: If your doctor suspects that you or your child has a genetic condition, this test can be done by taking a small amount of blood as usual. This does not require any special preparation.
• Prenatal Testing: If the baby's genes are being tested during pregnancy, the doctor will perform a test called ``amniocentesis,'' which involves taking a small amount of amniotic fluid from the mother's womb.
• Biopsy: If cancer is suspected, a small piece of tissue is taken from the tumor or bone marrow for testing (a bone marrow biopsy). Before a biopsy, your doctor will give you instructions on how to prepare for it, as anesthesia is required.
• Urine Test: A urine sample is sometimes used to diagnose or monitor bladder cancer.

What happens after receiving the test report?

It can usually take between one and four weeks to get the results of a FISH test. Your doctor will inform you of this time in advance.

If the result comes back 'positive' , it means that there is a genetic or chromosomal abnormality in your cell sample.

It's normal to feel scared and anxious when you see a result like this. But remember, this result is an opportunity to gain a clearer understanding of your condition. And, based on this information, your doctor will be able to decide on the most appropriate, targeted treatment for you.

For example, if this test detects a genetic mutation in a cancer, targeted therapy can be given to target that mutation, resulting in fewer side effects and more successful outcomes.

Therefore, instead of worrying about the results and worrying alone, talk to your doctor carefully and clearly understand what it means and what steps you need to take next.