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Know About Risk Factors

1 in 9 women in Canada is expected to develop breast cancer during her lifetime. That’s a striking statistic. But what does it mean to you?

In this section, Canadian Breast Cancer Foundation helps you navigate the topic of breast cancer risk with statistics and evidence-based facts that can help to inform your decisions about taking action to reduce the risk of breast cancer.

Assessing Your Risk By Risk Factors

A risk factor is something that increases a person’s chance of developing a disease. 

Established risk factors for breast cancer are determined by a body of research with conclusive evidence confirmed by different sources and studies. Risk factors are associated with an increased risk of breast cancer. This means that they have been linked to the development of the disease.

Breast cancer is a complex disease with many factors that interact in ways that are not yet fully understood.  While risk factors are established by conclusive research, they cannot be seen as rules or guarantees about whether or not a person will develop breast cancer. Evidence related to risk factors is based on patterns of disease that are observed in a population or large group of people, rather than individual cases. Even if you have several risk factors for breast cancer, this does not mean you will develop the disease.

On the other hand, some women who are diagnosed with breast cancer may appear to have no identifiable risk factors other than being a woman. Beyond risk estimates being based on what we observe in a large group of people, this tells us that there’s much more to be discovered about breast cancer and its causes.

In your own life, knowledge of risk factors can help you to put your own risk of breast cancer into perspective, encourage you to learn more, or motivate you to take action to reduce your risk. You may also find it helpful to speak to a health care provider to better understand your breast cancer risk.

Understanding Relative Risk 

Relative risk is a term used to describe how likely a person is to develop a disease when exposed to a specific factor, compared to someone who is not exposed to it. A factor can be anything a person comes into contact with, such as smoking, eating a diet high in fruits and vegetables, taking a medication, or being diagnosed with a health condition. These factors can increase, decrease, or have no effect on a person’s risk of developing a disease.

Relative risk is expressed as a number. It tells you by how much the risk of developing a disease is increased, or decreased, when a person is exposed to a factor.  When relative risk is greater than 1.0, a person’s risk for developing a disease is increased. 

Some examples of relative risk values and what they mean:

  • Relative risk = 1.3 means you have a 30% greater chance of developing the disease if you are exposed to risk factor compared to someone who is not exposed.

  • Relative risk = 1.9 means you have a 90% greater chance of developing the disease if you are exposed to risk factor compared to someone who is not exposed.

  • Relative risk = 2.0 means you have a 100% greater chance of developing the disease if you are exposed to a risk factor compared to someone who is not exposed. This is the same as saying the risk is 2x greater, or double, that of someone who is not exposed.

Selected Established Risk Factors For Breast Cancer

The following table lists of some of the established risk factors that increase a person’s risk of developing breast cancer, with some carrying more weight or a higher risk than others. Being female and aging are the strongest risk factors. Other risk factors are given with an estimate for how many times greater the risk is for someone who has the risk factor over someone who does not have it, all other factors being equal.

As a general rule:

Significant risk = a factor that increases a person's breast cancer risk by 3 times or more

Example: having had lobular carcinoma in situLobular carcinoma in situ (LCIS):
A condition where abnormal cells develop in the lobules of the breast. LCIS is not considered to be a true cancer, but is an indicator that a woman is at increased risk for developing invasive breast cancer in the future.
(LCIS) leads to a 7-12 times greater risk than a person who has not had LCIS.

Moderate risk = a factor that increases a person's breast cancer risk by 1.5–3 times

Example: starting menopauseMenopause:
A natural part of a woman's aging process, when the ovaries start to make less estrogen and progesterone and the menstrual periods stop. This change typically occurs between the late 40s and mid-to-late 50s.
later than age 55 leads to a 2 times greater risk than a woman who started menopause younger than 55.

Minimal risk = a factor that increases a person's breast cancer risk by 1-1.5 times

Example: being an unhealthy body weight leads to a 1-1.5 times greater risk than a person who is a healthier weight.

You may be tempted to add up all of the numbers for the risk factors that apply to you to determine your breast cancer risk. However, the relationship between individual risk factors is complex and determining your breast cancer risk is not as simple as adding them together.  You may wish to speak to a health care provider to better understand your breast cancer risk. They can use a breast cancer risk assessment tool to more accurately estimate your risk. These tools taken into account what is known to date about the interaction between risk factors.

Canadian Breast Cancer Foundation encourages you to use this information to think about breast cancer risk in terms of relative risk factors and lifestyle changes that can help to reduce your breast cancer risk.

The following table is a selection of known risk factors along with their effect on breast cancer risk (relative risk). You can learn more about any of these risk factors by clicking on them.

Risk factor Effect on breast cancer risk
(Relative risk)
Aging Very strong increase in risk
Being female Very strong increase in risk
BRCA1 or BRCA2 mutation 5-30 times greater risk
Personal History of Cancer  
   Hodgkin’s disease
   
   Invasive breast cancer or DCIS

15-25 times greater risk
1.5-10 times greater risk
Radiation exposure to the chest before age 30   
    Risk of breast cancer at age 40
   
    Risk of breast cancer at age 60

11 times greater risk
3.6 times greater risk
Dense breasts 4-6 times greater risk
Atypical hyperplasia 4-5 times greater risk
Family history of breast cancer   
    2 close family members with breast cancer
    Mother diagnosed before age 60
    Mother diagnosed after age 60

3-4 times greater risk
2-3 times greater risk

1.5-2 times greater risk
Combined HRT use 1.3-2.0 times greater risk
Combined birth control pill use 1.1-2.0 times greater risk
Not having children (compared with a woman who has her first child by age 35) 1.3 times greater risk
Not breast feeding 1.1-1.2 times greater risk
First period before age 12 1.2-1.3 times greater risk
Age 55 or older at menopause 1.3 times greater risk
Alcohol consumption (2-4 drinks per day) 1.2-1.4 times greater risk
Smoking 1.1-1.3 times greater risk
Lack of physical activity 1.1-1.2 times greater risk
Being an unhealthy body weight 1.2-1.6 times greater risk
 

Canadian Breast Cancer Foundation encourages you to learn more about your breast health, breast cancer risk factors, and ways to reduce your risk. To inform your decisions, we also encourage you to consider speaking with a health care provider. 


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 Cancer Society’s Steering Committee on Cancer Statistics.  Canadian Cancer Statistics 2014, Toronto, ON: Canadian Cancer Society, 2014.

Susan G. Komen. Risk Factors Summary Table of Relative Risks. Accessed February 12, 2014.