Genes and cancer

All cancers are caused by a change in genes or damage to genes. Genes are found in every cell in the body. Genes inside each cell tell it when to grow, work, divide and die. Genes are pieces of DNA found within chromosomes in all of our cells. When a gene changes or mutates (called a gene mutation), the instructions it gives to the cell can stop it from working properly. This can cause abnormal development in the body or a medical condition.

Genes act like on and off switches inside of our cells. They control how our cells work by making proteins, such as antibodies and enzymes, and messengers such as hormones. A gene’s proteins give the instructions to our cells that tell them when to grow, divide and die (a process called apoptosis). And each gene has instructions within its DNA that tells a cell how to make these proteins.

When genes work properly, they help protect us against cancer. But when there is a change in our DNA or damage to our DNA, a gene can mutate. A mutated gene doesn’t work properly because the instructions in its DNA get mixed up. This can cause cells that should be resting to divide and grow out of control, and this may lead to cancer. Gene mutations can also cause a cell to make too many proteins, abnormal proteins or not enough proteins.

Gene mutations happen in our cells all the time. Every time a cell divides there is a risk of a mistake being made when the cell makes a copy of its DNA. Our cells can usually find these mistakes and fix them before they are passed on to new cells. But sometimes cells can’t fix these changes, and the changes are passed on to new cells. The cells that have a gene mutation because of damaged DNA are the ones that can become cancerous. Since gene mutations build up over time, we have a higher risk of developing cancer as we get older.

Inherited and non-inherited cancers

Some cancers are caused by genetic changes we are born with and that are inherited from our parents. Cancers that are caused by inherited gene mutations are called inherited or hereditary cancers. People with inherited gene mutations have a higher risk of developing cancer, but it doesn’t mean they will develop cancer. But people who have inherited gene mutations linked to cancer tend to develop cancer more often and at an earlier age than the rest of the population. Of all cancer cases, only about 5% to 10% are caused by inheriting a certain gene mutation.

But many types of cancer have been linked to heredity including breast and colon cancer in adults and retinoblastoma in children.

Other cancers develop from genetic changes that happen during our lifetime. These are non-inherited cancers (also called sporadic or acquired cancers). They develop from gene mutations that happen when genes wear out as we get older or when we are exposed to something around us that causes cancer. Most cancers are non-inherited.

Expert review and references

Genetic changes and cancer risk

Most cancers are caused by genetic changes that happen mostly by chance and are not inherited. They are acquired sometime during a person’s lifetime. These genetic changes are called sporadic (spontaneous) or acquired mutations. Sometimes these mutations are errors that occur during cell division.

Cancer risk in families

Our families and genetics are something we can’t change. Learn how family genes can affect your lifetime risk of cancer.

Family cancer syndromes

Some cancers happen more often in some families than others. Learn which cancers are known to be hereditary.

Genetic testing

Genetic testing is a medical test that looks for changes in chromosomes, genes or proteins that are linked to cancer and other diseases. Genes that are linked to cancer are sometimes called cancer genes.

Using genes in diagnosis, prognosis and treatment

Researchers study genes to help them learn more about which ones may be linked to cancer. They have mapped all of the genes that make up humans (called the human genome). Doctors are now using the human genome and better gene-based tests to study DNA and better understand cancer.

Medical disclaimer

The information that the Canadian Cancer Society provides does not replace your relationship with your doctor. The information is for your general use, so be sure to talk to a qualified healthcare professional before making medical decisions or if you have questions about your health.

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