Tumor Suppressor Genes

What are tumor suppressor genes?

Tumor suppressor genes prevent cell growth that can lead to cancer. These genes make proteins that suppress the process that can lead to tumors. To suppress means to “stop” or “restrain.” The proteins prevent cells from multiplying and making more cells. They help your body press the brakes on cell growth.

But when tumor suppressor genes change (mutate), they stop making the proteins your body needs to press the brakes. As a result, cells can grow out of control and form a mass of cells (tumor).

This is why tumor suppressor genes are so important for doctors to know about. Finding mutations in a tumor suppressor gene helps providers diagnose cancer. It helps them assess cancer risk.

Types of mutations in tumor suppressor genes

Researchers have identified dozens of tumor suppressor genes that help prevent cancer. When these genes mutate, they can contribute to cancer growth. Examples include:

• TP53: This gene is so important when it comes to preventing tumors that it’s called “the guardian of the genome.” More than half of all cancers involve a mutated TP53 gene.
• RB1: RB1 is the first tumor suppressor gene researchers discovered. They found that changes led to retinoblastoma. It’s also associated with breast, lung and bladder cancer, among others.
• CDKN2A: Mutated CDKN2A genes show up in inherited forms of melanoma and pancreatic cancer.
• BRCA1 and BRCA2: Mutations in the BRCA1 or BRCA2 gene increase your risk of inheriting breast and ovarian cancer. These mutations also increase your risk of other cancers. These include pancreatic, prostate and male breast cancers.
• APC: People born with familial adenomatous polyposis (FAP) carry a mutated form of the APC gene. FAP is linked to several conditions that often lead to colon cancer.
• PTEN: Like BRCA1 and BRCA2, PTEN mutations are associated with PTEN hamartoma tumor syndrome (PHTS). PHTS increases your risk of several cancers, including breast, thyroid and endometrial cancers.

What do tumor suppressor genes do?

Tumor suppressor genes stop cells from forming tumors. They help regulate a complicated process called “the cell cycle.” To understand how this works, it may help to understand the relationship among DNA, genes and cells.

Each cell in your body contains DNA that houses your genes. A small percentage of your genes act as tumor suppressors. They contain the instructions cells use to make proteins that prevent cell overgrowth. Tumor suppressor genes:

• Keep cells from multiplying so fast that they form tumors
• Make sure old and damaged cells die when they’re supposed to
• Repair DNA damage so that genes with errors don’t get copied into new cells
• Keep cancerous tumors from spreading

When one or more genes change, they make abnormal proteins. Or they stop making the proteins altogether. The cells don’t get the instructions that tell them to turn off. Cells keep making more cells; eventually, creating cancerous tumors.

Why do people have mutated tumor suppressor genes?

Some people inherit abnormal tumor suppressor genes from one or both biological parents. Li-Fraumeni syndrome is an example of a condition that happens when you inherit a mutated copy of TP53. Even inheriting one mutated gene increases your cancer risk. Cancer usually develops when both copies of a tumor suppressor gene stop working. This is a concept known as the “two-hit hypothesis.”

Some people inherit one abnormal tumor suppressor gene from one parent and a normal one from the other. But at some point in life, the normal gene mutates. Often, a person doesn’t develop cancer unless both inherited copies carry a mutation.

Usually, people develop cancer when tumor suppressor genes mutate with age. These mutations can be triggered by:

• Age-related wear and tear
• Environmental exposures like tobacco smoke or radiation
• Random errors during cell division

Our bodies are like assembly lines running at full speed to make new cells with copies of our genes. Sometimes, mistakes happen somewhere along the line. And over time, if the process isn’t upgraded or improved, the line mistakes become more frequent. This includes mistakes that cause tumor suppressor genes to stop working correctly.

Are there tests that find mutations?

There are blood and saliva tests that can detect abnormal tumor suppressor genes. These tests don’t diagnose cancer directly. Instead, they identify whether you carry mutations that increase your risk. Your healthcare provider can advise you on what tests you may need based on your health and medical history.

What is the difference between a tumor suppressor gene and an oncogene?

Tumor suppressor genes put the brakes on cell growth, preventing tumors from forming. But when they mutate, cell growth continues unchecked. Oncogenes, in contrast, press the gas on cell growth. They tell cells to keep multiplying. Think of it this way: Tumor suppressor genes tell cells to “slow down,” while oncogenes tell them to “speed up.”

Both play a role in cancer development.