Gene changes and cancer cells

How genes affect cancer risk

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. As well as telling the cell what to do and when to grow and divide, genes provide the recipe for cells to make proteins. These proteins carry out specific functions in the body.

When a cell divides, it makes a copy of itself, including all the genes it contains. Sometimes copying mistakes can happen, causing changes (mutations or alterations) in the genes. If these mistakes affect the genes that tell the cell what to do, a cancer can grow.

Most gene changes that cause cancer build up during a person’s lifetime (acquired gene changes). Some people are born with a gene change that increases their risk of cancer (an inherited faulty gene, also known as hereditary cancer syndrome). Only about 5% of cancers are caused by an inherited faulty gene.

Targeted therapy drugs may act on targets from either acquired or inherited gene changes. See below for examples of both types of gene changes.

Testing for targeted therapy

To find out if the cancer contains a gene change that may respond to a particular targeted therapy drug, your doctor will take a sample from the cancer or your blood, and send it to a laboratory for testing. It may take from a few days to a few weeks to receive the results.

The testing may find specific mistakes in that cancer, whether they are acquired gene changes found only in the cancer cells, or inherited changes that are also present in normal cells. The testing may involve a simple test known as staining, or more complex tests known as genomic or molecular testing.

Family testing

If the cancer contains a faulty gene that may be linked to a hereditary cancer syndrome, or if your personal or family history suggests a hereditary cancer syndrome, your doctor will refer you to a family cancer service or genetic counsellor. They may suggest genetic testing.

Knowing that you have inherited a faulty gene may help your doctor work out what treatment to recommend. It could also allow you to consider ways to reduce the risk of developing other cancers, and it is important information for your blood relatives. Medicare rebates are available for some genetic tests. You may need to meet certain eligibility requirements.

Some gene changes linked to cancer

*May be involved in other cancers, but list includes the main cancers linked to these gene changes.