Genetics and cancer

If someone in your family gets cancer, does that mean you will too? In most cases, no.

Most cancers are caused by mistakes that have built up in that particular cell – for example, mistakes that occur in a breast cell may result in a breast cancer. These changes are not inherited and are not passed on.

For some cancers, having a strong family history of cancer may increase your risk of developing cancer, but this won’t always mean you have inherited a faulty gene linked to cancer – for example, the family history might be caused by environmental or lifestyle factors.

A small number of people have a greater risk of developing certain cancers, such as breast, ovarian or bowel cancer, because they do carry an inherited faulty gene. Only about 5% of all cancers are linked to inherited faulty genes.

→ READ MORE: Cancer Glossary: what does this word mean?

Click below to learn more about the complex links between genes and cancer:

Genes are like instruction manuals that tell cells how to make molecules called proteins. These proteins are essential to the functioning of cells and carry out specific functions in the body.

Genes are made up of DNA (deoxyribonucleic acid). Each human cell has about 20,000 genes, and most genes come in pairs, with one copy inherited from each parent.

When most people think of genetic testing, they are thinking of inherited faulty genes that may increase the risk of cancer. This is called germline testing. For example, inherited faults in BRCA1 and BRCA2 genes are now known to be linked to the development of hereditary breast and ovarian cancer.

Testing is available to families with a high risk of having inherited a faulty gene, based on a strong history of certain cancers in the family.

Testing involves taking blood and is carried out by specialist laboratories.

Even if an inherited faulty gene is found, it doesn’t mean you will definitely get cancer – it only shows that you have an increased risk.

Some cancers are common. In Australia, the most common cancers are breast, bowel, lung, melanoma and prostate. Most families can follow the cancer screening guidelines for the general population.

In some families, there may be a number of closely related family members with the same cancer, or family members who have been diagnosed at a slightly younger than average age (say, under age 50). These families may be at a moderately increased risk of developing cancer, and screening may start a bit younger (say, at age 40).

If you have a family history of cancer, talk to your doctor about what you can do to reduce your risk and when you should start screening tests.

Ask your cancer specialist if your family members should be tested. This will usually be recommended only if tests have shown that you carry an inherited faulty gene. Often the genetic mutation that causes a cancer is just a random event and your family members won’t have a higher than normal risk of developing that cancer.

If you have not been diagnosed with cancer, but you are worried about your family history, talk to your GP about the types of cancer that have occurred in your family and the age each person was when they got cancer. If your doctor thinks the cancers in your family may be linked to an inherited faulty gene, they may refer you to a family cancer clinic or genetic counselling service.

Testing a cancer is called somatic genetic testing. Usually, these genetic changes have occurred only in the cancer. This type of genetic testing can sometimes be used to help work out suitable treatment options. For more information, talk to your doctor or local family cancer centre.

Click on the links below to learn more about genetics and cancer:

Need to talk?

Call 13 11 20 to talk to a health professional Or email us your questions