Why does breast cancer occur?
Cell growth is controlled by a cell’s genes. Genes contain the information that determines how our cells grow and work throughout our lifetime. This information can be passed from one generation to the next (inherited).
Sometimes, genes in breast cells develop changes. This can cause the cells to grow out of control, leading to cancer. These genetic changes, which occur throughout life are not inherited. They occur more often in older people. Why this happens is not fully understood.
What's the risk?
The risk of getting breast cancer increases with age. One in eleven women will get breast cancer at some time during their lives.
There are many factors that influence a person's chances of getting breast cancer. The two most important are
- being a woman, and
- getting older.
Most women who get breast cancer are over the age of 50. A family history of breast or ovarian cancer is also an important risk factor.
What's meant by a family history of breast cancer?
You have a family history if any of your blood relatives have had breast cancer.
As breast cancer is common, some women will have a family history of cancer by chance alone but a small number with a family history may have inherited a changed gene in all their cells, which increases the risk of cancer. The women most likely to have inherited a changed gene are those with the strongest family histories of breast cancer.
Understanding your family history of breast cancer can help to identify your risk:
- most women have close to the average chance for the Australian population (1 in 11)
- some women have a moderately increased chance
- a small number of women have a high chance
How does family history affect your risk?
A woman could have a high chance of getting breast cancer if she has:
- Three or more close blood relatives on one side of the family (mother’s or father’s) with breast or ovarian cancer. OR
- Two or more close blood relatives on one side of the family, plus one or more of the following features on the same side of the family:
- breast and ovarian cancer in the same person
- breast cancer before the age of 40
- ovarian cancer before the age of 50
- more than one diagnosis of breast cancer in an individual
- breast cancer in a male relative
- Jewish ancestry OR
- A family member who has had a genetic test that's shown an inherited change in a gene associated with breast or ovarian cancer.
Inheriting a breast cancer gene change
Breast cancer caused by inheriting a changed gene is called hereditary cancer. We all inherit a set of genes from each of our parents. Sometimes there's a change (called a mutation) in one copy of a gene which stops that gene working properly.
There are several genes for which inherited changes may be involved in the development of both breast and ovarian cancer. These are genes which normally control cell growth and prevent a woman getting breast or ovarian cancer. Some of these are genes that you may have heard called BRCA1 and BRCA2. Their names come from the abbreviation of 'breast cancer 1' and 'breast cancer 2'. Both men and women can inherit a change in these genes. Genetic testing is available for women and men who know that a blood relative carries a change in BRCA1 or BRCA2. This can be arranged at a family cancer centre.
If a woman has inherited a change in one of these genes, she has a higher chance of breast or ovarian cancer but that doesn't mean she's certain to get cancer. Less than 5% of all breast and ovarian cancers can be explained by an inherited gene change in BRCA1 or BRCA2.
What can you do?
The earlier a cancer is found the more successful treatment is likely to be. We make the following recommendations.
All women should be aware of changes in their breasts and visit a doctor promptly with any unusual changes such as:
- any change in the size or shape of the breast
- a lump in or close to the breast
- any change in the nipple, such as a discharge
Women over 50 are encouraged to have a mammogram every 2 years. Free mammograms are provided by BreastScreen (13 20 50) and a doctor's referral is not needed. However women should understand the limitations of the test and make an informed personal choice about taking part in breast screening.
Women with a family history should talk to their doctors. It may be appropriate for some women with a strong family history to be referred to a family cancer centre where their risk of breast or ovarian cancer, based on their family history, can be worked out and talked about in more detail. They can discuss types of screening that are available and talk about the recomendations for their family with a specialist.
For more information, call Cancer Council on 13 11 20. If you're worried about your risk of breast cancer based on your family history contact your doctor or nearest family cancer centre.