Tumor Suppressor Genes

What are tumor suppressor genes?

Tumor suppressor genes are among the most common genes protecting your body from cancer. These genes make special proteins that put the brakes on cell growth that may cause cancer. When tumor suppressor genes mutate (change), it’s as if they switch from pressing on the brakes to hitting the gas pedal, suddenly putting cell growth into overdrive.

What do tumor suppressor genes do?

To understand what tumor suppressor genes do, it may help to understand the relationship between DNA, genes and cells.

You have genes in the DNA of each of the trillions of cells in your body. Genes tell cells what to do, including when to multiply and when to stop multiplying.

When one or more genes in a cell mutate, or change, the mutated genes stop making proteins or make abnormal proteins. When that happens, the abnormal proteins may stop giving cells instructions or give cells new instructions. In cancer, cells following new instructions begin to multiply uncontrollably, eventually creating cancerous tumors. Tumor suppressor genes help regulate a complicated cellular timetable, sometimes called the cell cycle. Tumor suppressor genes:

• Keep cells from dividing too fast and multiplying so quickly that they form tumors.
• Make sure cells, which typically live for a set time, only live as long as they’re supposed to live. This is “programmed” cell death (apoptosis).
• Repair DNA damage that can happen when cells divide more quickly than usual.
• Keep cancerous tumors from spreading (metastasis).

Why do people have mutated tumor suppressor genes?

Some people inherit abnormal or mutated tumor suppressor genes from their biological parents. That means the egg or sperm that creates your cells carried mutated genes. Li-Fraumeni syndrome is an example of a condition that happens when you inherit a mutated tumor suppressor gene.

Some people born with one mutated tumor suppressor gene develop another later on in life. Having two mutated genes increases their risk of developing certain cancers, including breast cancer. Still, simply inheriting these genes doesn’t mean a person will have cancer.

In general, however, tumor suppressor genes typically mutate, or change, as people grow older. Our bodies are like assembly lines running at full speed to produce new 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. That includes mistakes that cause tumor suppressor genes to stop working.

What are examples of mutations in tumor suppressor genes?

Medical researchers have identified more than 1,000 types of tumor suppression genes that cause cancer when they mutate. Common examples include:

Tp53 (p53)

Mutations in the p53 gene are linked to more than 50% of all types of cancer.

RB1

The RB1 gene is the first known example of mutations in a tumor suppressor gene that cause cancer. Research shows people who develop common cancers such as breast cancer and prostate cancer carry mutated RB1 genes.

CDKN2a

People who have the inherited conditions of familial melanoma and familial pancreatic carcinoma carry mutated CDKN2a genes. This genetic mutation shows up in about 25% to 30% of different cancers people develop during their lifetimes, including breast cancer, lung cancer, bladder cancer and pancreatic cancer.

BRCA1

The mutated BRCA1 gene is found in people with inherited breast and ovarian cancer and in ovarian cancer that develops during their lifetimes. People with inherited breast cancer may carry a related gene, BRCA2. These mutations increase the risk of developing breast, ovarian and other types of cancer. In some cases, healthcare providers may recommend genetic testing for people with a family history of breast or ovarian cancer.

APC

People born with Gardner syndrome or Turcot syndrome carry a mutated form of the APC gene. Researchers have linked mutated APC genes to cases of colorectal cancer and hepatocellular carcinoma (liver cancer).

PTEN

People with different types of cancer such as breast cancer, prostate cancer, head and neck squamous carcinoma, and follicular thyroid cancer carry mutated PTEN genes.

Are there tests that find mutations in tumor suppressor genes?

Yes, there are tests to identify some genetic mutations, including mutations in some tumor suppressor genes. But not everyone is a candidate for these tests. According to the National Cancer Institute, factors that may indicate you would benefit from having genetic testing for cancer include:

• You were diagnosed with cancer before age 50.
• You have several different kinds of cancer.
• You have cancer in both sets of an organ, such as cancer in both of your kidneys or both breasts.
• Several first-degree family members have the same type of cancer. First-degree family members include your biological parents, siblings or children. Some researchers advocate for testing second-degree and third-degree family members.
• Several of your family members have or have had cancer.
• You have a specific cancer type that usually doesn’t happen in people your age or sex. Male breast cancer is an example of an unusual instance of a specific cancer type.
• You have physical differences linked to certain inherited cancer syndromes. For example, neurofibromatosis Type 1 is an inherited cancer that also causes other symptoms such as noncancerous tumors called neurofibromas.
• You’re a member of a racial or ethnic group that’s known for having certain inherited cancer syndromes AND you have one or more of the factors listed above. For example, studies show BRCA1/2 mutations are more common in people who are of Ashkenazi (Central and Eastern European) Jewish ancestry.

It’s important to remember you may not get clear answers if you have genetic testing for cancer. It’s also important to remember carrying a genetic mutation doesn’t mean you’ll have cancer. It may mean you have an increased risk of cancer.

If you’re concerned about your risk of developing cancer, ask your healthcare provider to evaluate your overall health, your lifestyle habits and your family medical history. They can recommend specific cancer screening tests. The screening tests may not involve genetic testing.