Cancer genetics

Cancer develops because of changes (variants) in genes. Genes contain DNA, which provides instructions for how cells grow, divide and function. When gene changes occur, they can affect how cells behave and sometimes allow cancer to develop.

Gene changes can be inherited from a parent or acquired during a person's lifetime. Most cancers are caused by gene changes that occur during life, but some are linked to inherited gene changes.

Cancer genes

Some genes play an important role in protecting the body from cancer. These are sometimes thought of as ‘cancer protection genes’. When these genes are working properly, they help control cell growth, repair damaged DNA and prevent abnormal cells from becoming cancerous.

A variant in one of these genes can reduce or change how well it works. This may increase the likelihood of developing certain types of cancer because cells are less able to control growth or repair DNA damage. However, having a variant in a cancer protection gene does not mean a person will develop cancer. It means their risk may be higher compared to the general population. More detail is provided in this factsheet.

Germline gene changes

Some gene changes are inherited from a parent and can be passed down through a family. These are called germline variants.

Germline variants are present in reproductive cells (sperm or egg cells). This means they can be passed from parents to children. Because they are present from conception, germline variants are usually found in every cell of a person's body.

If you have a germline variant in a cancer gene it could increase the chance of developing certain types of cancer. It does not mean you will develop cancer. Identifying the variant early can help access screening to detect cancer early in people without symptoms.

Talk to your GP if you have a strong family history of cancer or if an inherited cancer gene variant has been identified in your family.

Somatic gene changes

Sometimes, a gene change appears for the first time in a person with no family history. These are called somatic variants and are not inherited from parents.

Somatic variants occur after conception in the body's cells (not in sperm or egg cells). Because of this, they cannot be passed from parents to children.

Some somatic variants can occur by chance as cells grow and divide, while others are caused by environmental or lifestyle factors that damage DNA. For example, too much ultraviolet (UV) radiation from the sun can damage DNA in skin cells and contribute to the development of skin cancer.

Genetic testing is a tool that looks at your genes. It is a way to find variants that may cause a genetic condition or increase the chance of developing one, including cancer.

Somatic genetic testing

Somatic genetic testing (testing of non-inherited cells) looks for variants that occur after conception. These variants are not inherited from parents.

This type of testing usually uses DNA taken from a tumour. The results can help guide personalised cancer treatment, like choosing the most effective medication. Sometimes, testing DNA from a tumour can reveal a germline gene change. If this happens, you should be referred to a genetic health professional to discuss the result and further testing.

Germline genetic testing

Germline genetic testing looks for inherited genetic variants. This type of testing uses DNA from a sample of blood or saliva. The results can help to:

• understand why you developed cancer
• assess your chance of developing cancer if you have not already been diagnosed
• guide screening or preventative care
• help relatives access predictive testing (sometimes called cascade screening).

You don’t need to remember all this information. Your healthcare professional can explain the testing to you, and what the results mean for you and for your relatives.

It is important that you provide informed consent before genetic testing. There is more information in the information sheet about consenting to genetic and genomic testing.

Ordering a genetic test requires specialist knowledge and genetic counselling. For people without a cancer diagnosis, certain criteria may need to be met before a test can be offered.

Genetic health professionals

Clinical geneticists (doctors with specialised training in genetics) can order genetic tests. You may also meet with a genetic counsellor who will explain the benefits, risks and limitations of testing and support you in making an informed decision about testing.

Genetic testing from genetic health professionals may be recommended to:

• investigate a possible inherited cause of cancer
• assess the chance of developing cancer in the future.

Specialist doctors

Some specialist doctors who are involved in cancer care can also order genetic tests. These may include oncologists, surgeons or gynaecologists. In this setting, genetic testing is often used to help guide cancer treatment and management decisions, such as choosing targeted therapies.

A cancer diagnosis, for you or someone you know, can bring up a range of challenging emotions. You are not alone in feeling this way, and there is lots of support available.

• The Cancer Council WA aims to support West Australians’ journeys with cancer, from the point of diagnosis to life after cancer.
• Inherited Cancers Australia is a national charity dedicated to supporting families with, or at risk of inherited cancers.

You can also talk to your GP. Genetic Health WA can help with understanding genetic testing for cancer, even if you don’t have cancer but there is history of cancer in your family.

Cancer screening is designed to detect cancer early in people without symptoms. Finding cancer at an early stage often makes it easier to treat. Regular screening is important as your body changes over time. However, if you are worried or have symptoms, you should see a doctor instead of waiting for screening.

Population cancer screening programs are aimed at sections of the general population. The programs are for people without a known genetic variant increasing their risk of cancer. If you have an inherited genetic variant that increases your risk of cancer, talk to your healthcare professional about personalised screening recommendations.

Key population cancer screening programs include:

• Bowel cancer screening. At-home bowel screening tests are sent to people aged 45-74 years every two years.
• Cervical screening. A cervical screening test is recommended every five years for women and people with a cervix aged 25–74 years.
• Breast screening. BreastScreen WA provides screening mammograms to women 40 years or over with no breast symptoms. BreastScreen WA specifically targets women aged 50-74 years.
• Lung cancer screening. Low-dose computed tomography (CT) scans of the chest are targeted at high-risk individuals aged 50-70 years with a significant smoking history.

These programs are free or subsidised (meaning there might be a small cost). More information about cancer screening is available from the Department of Health, Disability and Ageing.