All women are at some risk of developing breast cancer. But some women are at a higher risk than others. Understanding your level of risk can help you make informed decisions about breast cancer screening and lifestyle changes to help reduce your risk.

Risk categories can help inform women and their health care providers about options for breast cancer screening and risk reduction. The most commonly used risk categories are average risk  and high risk.  A third, less commonly used, category is that of intermediate risk. Most Canadian women are at average risk of breast cancer.

Within each risk category, a woman’s risk of breast cancer depends on her age and other risk factors.  A risk factor is something that increases a person’s chance of developing a disease. Established breast cancer risk factors are backed up by a body of research with credible evidence that is confirmed by different sources and studies. 

Average risk of breast cancer

The majority of Canadian women (approximately 80 per cent) are at average risk of developing breast cancer in their lifetime. Average risk means that over their lifetime they have a one in nine chance, or 11 per cent risk, of developing breast cancer.

• Women at average risk have the key risk factors for breast cancer (gender and ageing) but none of the risk factors listed for high or intermediate risk of breast cancer.

Screening research shows that breast cancer mortality is reduced when women at average risk have an annual mammogram starting at the age of 40.

High risk of breast cancer

A small number of Canadian women (approximately 1-2 per cent) are at high risk of developing breast cancer in their lifetime. High risk means that over their lifetime they have at least a one in four chance, or 25 per cent risk, of developing breast cancer. In the case of rare genetic mutations, this risk can be at least as high as a one in two chance of developing breast cancer.

Women at high risk include those with one or a combination of the following risk factors:

• A confirmed carrier of a genetic mutation that increases the risk of breast cancer, (e.g. BRCA 1 or BRCA 2).   "Confirmed" means the person has had genetic testing and a genetic mutation was found. They may not have breast cancer but they "carry" the genetic mutation and are at a higher risk of developing the disease.

• Untested first degree relative (parent, sibling or child) of a confirmed carrier. "Untested" means a person who has not yet had genetic testing or has chosen to decline it.

• A family history of breast cancer, including a hereditary breast syndrome and 25 per cent or greater lifetime personal risk of breast cancer. This is confirmed by genetic counselling when a risk calculation is made based on a model of family breast cancer history.

• A personal history of breast cancer.

• A personal history of high radiation exposure to the chest before the age of 30  (e.g. cancer treatment with radiation therapy to the chest).

Based on screening research, women who are at high risk of developing breast cancer are advised to consider breast cancer screening by the age of 30, but not before 25. 

Intermediate risk of breast cancer

Some Canadian women (approximately 18 per cent) are at intermediate risk of developing breast cancer in their lifetime. Intermediate risk means that they have at least a one in seven chance, or 15 per cent risk, up to a one in four chance, or 25 per cent risk, of developing breast cancer in their lifetime.

Women are considered intermediate risk if they have clinically diagnosed breast density and one of the following risk factors:

• A personal history of breast cancer(with no known/suspected genetic mutation).

• A prior high-risk lesion and not currently on chemoprevention.

• An intermediate family history of breast cancer.

Make an informed decision about what is right for you.  If you think you may be at intermediate risk of breast cancer, the Canadian Breast Cancer Foundation encourages you to speak to a health care provider about your breast cancer risk, ways to reduce your risk, and your options for breast cancer screening.

More Information:

Genetic counselling and testing

Breast cancer screening by mammography

Understanding breast cancer risk

Using risk assessment tools

Breast cancer risk factors

Reducing your risk of breast cancer  

Sources:

Canadian Breast Cancer Foundation. (2010). Earlier Detection and Diagnosis of Breast Cancer: A Report from It’s About Time! A Consensus Conference. Toronto, ON: Canadian Breast Cancer Foundation. 

Canadian Breast Cancer Foundation. (2010). Earlier Detection and Diagnosis of Breast Cancer. Recommendations and Scientific Review from It’s About Time! A Consensus Conference. Toronto, ON: Canadian Breast Cancer Foundation. 

Canadian Cancer Society’s Steering Committee on Cancer Statistics.  Canadian Cancer Statistics 2011, Toronto, ON: Canadian Cancer Society, 2011. Accessed July 31, 2011.