All women are at some risk of developing breast cancer, but some are at a higher risk than others. Understanding your level of risk can help you make informed decisions to reduce your risk of breast cancer.

Breast cancer risk falls into several categories. The most commonly used risk categories are average risk and high risk. A third and less commonly used category is intermediate risk. These categories can help inform women and their health care providers about options for breast cancer risk reduction and screening for earlier detection.

Within each category, a woman’s risk of breast cancer depends on her age and other risk factors.

Average risk of breast cancer
Most Ontario women (approximately 80%) are at average risk of breast cancer. Over their lifetime they have a one in nine chance, or 11 per cent risk, of developing the disease.

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

If you think you may be at average risk of breast cancer, we encourage you to learn more about your risk level, breast cancer risk factors, and the concrete steps you can take now to reduce your risk. We also encourage you to consider discussing these issues with a health care provider, and to ask about your screening options for the earlier detection of breast cancer.

High risk of breast cancer
A small number of Ontario women (approximately 1-2%) 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 the disease. In the case of rare genetic mutations, this risk can be at least as high as a one in two chance.

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 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).

If you think you may be at high risk of breast cancer, we encourage you to speak to a health care provider about genetic counselling, genetic testing, ways to reduce your risk, and your screening options for the earlier detection of breast cancer.

Intermediate risk of breast cancer
Some Ontario 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, and up to a one in four chance, or 25 per cent risk, of developing the disease in their lifetime.

Women are considered to be at 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.

If you think you may be at intermediate risk of breast cancer, we encourage you to speak to a health care provider about your breast cancer risk, ways to reduce your risk, and your screening options for the earlier detection of breast cancer.

Explore this website to learn more about breast cancer risk factors and the many concrete steps you can take now to benefit your breast health and reduce your risk of breast cancer.

Join us in the campaign to stop breast cancer before it starts. Encourage people in your life to join the campaign too.