Our bodies are amazing machines. They have many defense systems that protect us from diseases that come from outside and also control problems that arise within the body. Similarly, there are special "guards" in our genes that help stop the growth of cancer cells. Today we are going to talk about them.
What are these tumor suppressor genes?
Simply put, these are genes that stop cells from growing out of control, which can lead to cancer. These genes produce special proteins. These proteins are what stop the process of forming tumors. In other words, these genes act like a "brake system" that controls the speed at which cells in our body divide.
Imagine you're driving a car. You need the brakes to control the speed of the car, right? That's how it is. The cells in our body need to divide as much as they need to, and then stop dividing when they need to. The function of applying these "brakes" is done by proteins made by tumor suppressor genes.
But, what happens if for some reason these genes change, that is, a mutation ? It's like the brakes on a car breaking. When the brakes stop working, the production of proteins that tell cells to stop dividing stops. Then the cells start dividing uncontrollably. The clump of cells that accumulates in this way is what we call a "tumor."
This is why it is so important for doctors to be aware of these tumor suppressor genes. Testing for mutations in these genes can help determine the cause of a person's cancer and also assess cancer risk.
What are the main mutations seen in these genes?
Researchers have now identified dozens of tumor suppressor genes that help prevent cancer. Mutations in these genes can contribute to the development of cancer. Let's look at a few examples. I've put this information in a table below to make it easier to understand.
| Gene Name | Related cancers and significance |
|---|---|
| TP53 | This is so important that scientists call it "the guardian of the genome." More than 50% of cancers in the world are linked to mutations in the TP53 gene. |
| RB1 | This is the first tumor suppressor gene discovered by researchers. Mutations in this gene cause retinoblastoma , a cancer of the eye. It is also linked to breast, lung, and bladder cancers. |
| CDKN2A | Variations in this gene can be seen in hereditary skin cancer (melanoma) and pancreatic cancer . |
| BRCA1 and BRCA2 | You've probably heard of these two names. Variations in these genes significantly increase the risk of hereditary breast and ovarian cancer. They also increase the risk of pancreatic, prostate, and male breast cancer. |
| APC | People born with Familial Adenomatous Polyposis (FAP) , an inherited condition, have a mutated copy of the APC gene. This condition often leads to colon cancer. |
| PTEN | Like the BRCA gene, mutations in the PTEN gene are associated with a condition called PTEN hamartoma tumor syndrome (PHTS) , which increases the risk of several types of cancer, including breast, thyroid, and uterine cancer. |
What exactly is the role of these genes?
The main function of these genes is to stop cells from clumping together and forming tumors. To understand how that happens, we need to understand a little about the relationship between DNA, genes, and cells.
Imagine that every cell in our body is like a small factory. All the instructions needed for this factory are in a big library. This library is called DNA . The books in that library are called genes . Each book (gene) contains a "recipe" for making a certain protein that the body needs. So, the books called tumor suppressor genes contain the recipes for making proteins that stop cells from growing.
These genes perform several main functions:
- It prevents cells from dividing rapidly and uncontrollably, leading to the formation of tumors.
- It causes old, damaged cells to die at a certain time. This is a normal process in the body.
- Damage to DNA is repaired, which prevents the faulty genes from being copied into new cells.
- It helps prevent cancer from spreading to other parts of the body.
So, if there is a change in this one gene, the protein it produces can be made incorrectly. Or the protein can stop being made completely. Then the cells don't get the message "stop dividing now." The result is that the cells continue to divide and form cancerous tumors.
Why do these cancer-suppressing genes mutate?
There are two main reasons why someone's tumor suppressor genes may change.
1. Inheritance from generation to generation
Some people inherit these mutated genes from their parents. For example, Li-Fraumeni syndrome is a condition caused by inheriting a mutated copy of the TP53 gene. Normally, we have two copies of each gene (one from our mother, one from our father). In this way, inheriting just one mutated copy increases the risk of cancer.
Normally, for cancer to develop, both copies of a gene must be inactivated. This is also known as the "two-hit hypothesis." This means that if one copy is inherited with a defect and the other healthy copy changes during life for some reason, cancer can develop.
2. Occurrence during life
Many people develop cancer because of changes in these genes that occur with age. These can be caused by:
- Natural changes that occur in the body with aging: Just like the parts of an old machine wear out.
- Environmental factors: exposure to tobacco smoke, various chemicals, or radiation.
- Random errors during cell division: Our body is like a factory that works non-stop. New cells are being produced all the time. Sometimes mistakes can happen during this process. These mistakes can accumulate over time.
Are there tests to detect changes in these genes?
Yes, there are blood and saliva tests that can detect abnormalities in these tumor suppressor genes. But there's something very important to understand here.
These tests do not directly diagnose cancer. Instead, they only identify whether you have a genetic mutation that increases your risk of cancer.
Only your doctor can best advise you on whether you need this type of test, given your health and family history. Therefore, it is best to talk to your doctor about it.
What is the difference between Tumor Suppressor Genes and Oncogenes?
Although both of these genes are involved in causing cancer, they work in opposite ways. Let's go back to our car example.
- Tumor Suppressor Genes are like the brake pedal on a car. They stop cell growth. If one of these genes changes, that is, if the brake breaks, the cell growth cannot be stopped.
- Oncogenes are like the accelerator pedal in a car. They tell cells to "speed up" their growth. If one of these genes changes, that is, if the accelerator gets stuck, the cells start dividing rapidly and uncontrollably.
One or both of these two ways of causing cancer can affect you. That is, you can imagine what would happen if the brakes broke and the accelerator jammed.
Take-Home Message
- In our own body, there are special genes (Tumor Suppressor Genes) that act like a "brake system" that stops the growth of cancer cells.
- Changes (mutations) in these genes can be inherited or occur during life.
- Normally, for cancer to develop, there must be some defect in both copies of this gene.
- Finding out that you have this kind of change through a genetic test does not mean that you have cancer, but it does mean that your risk of cancer can be assessed.
- Always talk to your doctor about your family cancer history and your personal risk.
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