Cancer & genetics

Cancer is the term used for when cells in the body become abnormal and grow out of control.

Our bodies are always making new cells: so we can grow, to replace worn-out cells, or to heal damaged cells after an injury. This process is controlled by certain genes. Each person has a set of many thousands of genes passed on (inherited) from both parents. Genes are found in every cell of our body. All cancers are caused by changes to these genes.

Changes to our genes usually happen during our lifetime, although a small number of people inherit such a change from a parent.

How can changed genes cause cancer?

Everyone has some changed genes. Usually they don’t cause us any problems. Sometimes, however, our changed genes make us more likely to develop particular health problems, including cancer.

Normally, cells grow and multiply in an orderly way. However, changed genes can cause cells to behave abnormally. They may grow into a lump. These lumps can be benign (not cancerous) or malignant (cancerous).

If you have inherited a changed gene you will not definitely develop cancer. Cancers arise through a succession of changes in gene activity in a cell. Your risk will vary depending on which type of cancer runs in your family, and other factors including your age, gender and lifestyle.

What types of cancer can be due to an inherited changed gene?

A small number of families have an increased risk of the following cancers because they carry a changed gene:

In rare cases there may be a number of people in a family who have less common cancers in a way that suggests an inherited changed gene is present. It is therefore important to look at all the different types of cancer that have occurred in the family.

It is estimated that 5% to 10% of the common cancers in Australia may be due to a changed gene passed on from a parent.

Is my family history a concern?

Look at the family history on your father’s and your mother’s side. The clues that cancer in the family may be due to an inherited changed gene include:

The number of relatives (related by blood not marriage) who had cancer. The more blood relatives who have had cancer – in particular breast, ovarian and/or bowel cancer – the more likely the cancer is due to an inherited changed gene.
The ages at which cancers in the family developed. The younger people are when they develop cancer – compared to the general community – the more likely it is to be due to an inherited changed gene.
The pattern of cancer in the family. The types of cancer and who it affects in the family are important. In some families a number of blood relatives have the same type of cancer. In others, there may be more than one kind of cancer in the family. This is because some changed genes can cause more than one type of cancer.

The more clues that are present, the more likely it is that there is an inherited changed gene in the family. However, it is not definite. Remember – even if you do have a changed gene, it does not mean you will develop cancer.

If you are worried about your family history of cancer please contact your doctor or nearest family cancer centre.