Am I at Risk of Developing Breast Cancer?

Despite scientific and medical advances, the causes of breast cancer remain unknown. According to experts, there is no one single cause or trigger for it. Nonetheless, studies have shown that certain factors increase the chances of developing breast cancer, sex and age being the predominant risk factors. Others may have an impact, but only for a minority of breast cancer cases.

Estrogen exposure

One of the main risk factor is the effect of certain female hormones, particularly estrogens, which may promote the development of certain types of breast cancer. Therefore, anything that can increase the amount of estrogen in the body or increase the length of time the body is exposed to estrogen is also a factor.

This increase in estrogen or in exposure to it occurs notably with early menstruation, taking oral contraceptives, a late first pregnancy or no pregnancy at all, not breastfeeding, late menopause, prolonged treatment with hormone replacement therapy for menopause, obesity and alcohol consumption.

Other factors can be divided into two categories: nonmodifiable factors (hereditary factors) and modifiable factors (factors that we can influence). The section below summarizes the main risk factors.

Nonmodifiable risk factors:

  • Being female
  • Age
  • Personal history of breast cancer
  • Family history of breast cancer
  • Genetic mutations (BRCA1, BRCA2, etc.)
  • Early menstruation (before the age of 12)
  • Late menopause (after the age of 55)
  • High breast density

Modifiable risk factors:

  • (lifestyle causes)
  • Alcohol consumption
  • Obesity (especially among postmenopausal women)
  • Sedentary lifestyle (lack of physical activity)
  • Early exposure to ionizing radiation
  • Hormone replacement therapy
  • Late first pregnancy (after the age of 30) or no full-term pregnancy

Nonmodifiable risk factors

Nonmodifiable risk factors refer to biological factors over which women have no control, unlike modifiable risk factors.

Breast cancer risk factors

Being a woman is in itself a risk factor since more than 99% of breast cancer cases develop in women. The disease appears in men in less than 1% of cases, and often over the age of 60.

The risk of breast cancer increases with age. The longer a woman lives, the greater the likelihood she will develop the disease in her lifetime. This type of cancer is more common among women aged 50 to 69. However, in almost one out of five cases, it affects women aged 20 to 49. In about 20% of cases, it is diagnosed in women over the age of 70.

Women who have already had breast cancer are at greater risk of recurrence, be it in the same breast or in the other.

The risk of developing breast cancer increases if family members on either the paternal or maternal side have had breast cancer, especially if they are female and if the diagnosis was made before menopause. The greater the number of first-degree family members (father, mother, sister or daughter) who have had breast cancer, the greater the risk.

The woman’s risk is lower for second-degree relatives (grandmother, aunt or niece), but it is higher if the family member had cancer in both breasts (bilateral breast cancer) before menopause. The following family history scenarios are also considered risk factors:

  • Two or more family members with breast or ovarian cancer
  • A family member with both breast and ovarian cancer
  • A male family member with breast cancer

It should be noted, however, that most affected women do not have a family history of the disease. Be vigilant: If there is a history of breast cancer in your family, talk to your doctor.

The genes we inherit can mutate over the generations and increase the risk of developing cancer. 

If you have questions about genetics and breast cancer risk, please contact Nathalie Bolduc, Certified genetic counsellor, at nbolduc@rubanrose.org.

A woman who starts menstruating early (i.e., before the age of 12) is exposed to estrogen and other hormones longer, which increases her risk of breast cancer.

Late menopause (i.e., after age 55) lengthens a woman’s exposure to estrogen during her lifetime. This increases her risk of developing breast cancer.

Modifiable risk factors

Breast cancer risk factors

In addition to genetic or biological risk factors, certain behaviours or lifestyle habits can increase the risk of breast cancer. Because these habits can be changed, these risk factors are considered modifiable.

In some cases, it may be difficult to give up certain practices to reduce the risk of breast cancer. For example, hormone replacement therapy may be desirable for a woman with severe menopausal symptoms. It is best to discuss your risk factors with a doctor so you can make the best decisions for your health.

Having received radiation or ionizing radiation for medical treatment is a risk factor for breast cancer. This risk is higher if the treatment was given with chemotherapy at puberty or before the age of 15.

Doctors may prescribe hormone replacement therapy (HRT) to lessen severe side effects of menopause. This treatment is sometimes combined with another hormone, a progestin, which is a synthetic form of progesterone.

While HRT generally relieves women of the side effects of menopause, it may also increase the risk of breast cancer, given that it is made up of estrogen, a hormone linked to the disease. Studies have shown that the risk of developing breast cancer increases after hormone replacement therapy is used for five years or more, and even more so if this treatment also contains a progestin.

The increased risk seems to disappear within a few years after the treatment. However, many researchers believe that the risks of long-term hormone replacement therapy, combined with progestin, outweigh the treatment’s benefits.

Women experiencing the severe effects of menopause should work with their doctor to make the best choice for their health, deciding whether or not to take HRT based on the adverse symptoms of menopause and personal risk factors for breast cancer.

Regardless of their choice, it is strongly recommended that pre- or post-menopausal women regularly observe their breasts for any abnormal changes (lumps, redness, orange peel skin, etc.). It is important to remember that the risk of developing breast cancer increases with age. In addition, it is strongly recommended that women between the ages of 50 and 69 years have a screening mammogram every two years.

During pregnancy, a woman’s breast cells temporarily stop being exposed to circulating estrogen. As a result, the more pregnancies a woman has had, the less she has been exposed to this breast cancer-related hormone, unlike women who have never been pregnant.

Furthermore, women who had their first pregnancy after age 30 have a slightly higher risk of cancer than women who had their first full-term pregnancy before this age.

Breastfeeding reduces the exposure of breast cells to estrogen and therefore protects women from developing breast cancer. According to many studies, breastfeeding is considered a protective factor against breast cancer.

The breasts are said to be dense when they consist of more connective tissue, glands and ducts than fat (adipose) tissue. Only a mammogram can determine breast density. Mammography makes it possible to see the contrasts between dense radiopaque tissue (in white) and radiotranslucent fatty tissue (in grey).

Here is an example of a low-density breast and a very dense breast:

Women with dense breast tissue have a greater risk of developing breast cancer than other women. Breast density decreases with age and after menopause. However, breast density is a modifiable factor, as it can be influenced by our lifestyle habits. For example, the use of hormone replacement therapy, a late first pregnancy, no full-term pregnancy and alcohol consumption may increase breast density. Conversely, taking vitamin D may decrease breast density, thus reducing the risk of developing breast cancer.

Drinking even small amounts of alcohol increases the risk of developing breast cancer. This risk increases proportionally with the amount consumed. There are two possible explanations for this risk:

  • Alcohol may increase the level of estrogen, a hormone associated with breast cancer.
  • Alcohol may also reduce essential nutrients, such as folic acid (a type of vitamin B), and vitamins A and C, all of which protect against cellular lesions.

It is recommended to limit alcohol consumption to one drink per day for a maximum of five days per week.

Obesity increases the risk of developing breast cancer in postmenopausal women. After menopause, fatty tissue produces some estrogen. Increased levels of this hormone are associated with breast cancer.

Research indicates that not exercising is a risk factor for breast cancer. Conversely, these studies have also shown a link between regular physical activity and a decreased risk of developing the disease. Engaging in high-intensity physical activity for more than four hours per week reduces this risk. The effect of exercise on breast cancer risk may be greater in premenopausal women with normal or low body weight.

Other risk factors

Genetic mutations

Genetic mutations cause about 5-10% of breast cancers. The genes we inherit may have mutated over the generations and in this way may increase the chances of developing cancer. However, only a small number of breast cancers, about 5-10%, would be due to a known genetic mutation.

BRCA1 and BRCA2 are the most commonly known genes associated with breast cancer. Mutations in these genes make some women more likely to develop breast cancer. Mutations in various genes (ATM, CDH1, CHEK2, MRE11A, MSH6, NBN, PALB2, PMS2, PTEN, RAD50, RAD51C, SEC23B or TP53) have also been associated with increased breast cancer risk.

Fortunately, important studies are underway to better characterize which mutations increase the odds of developing breast cancer. Eventually, it may be possible to associate a genetic profile with a level of risk, allowing for early follow-up and management of high-risk women.

Other genetic disorders

Some other rare hereditary genetic disorders also increase the chances of breast cancer: Li‑Fraumeni syndrome, ataxia-telangiectasias, Cowden syndrome, Peutz-Jeghers syndrome.

If you are concerned about the risk of breast cancer due to hereditary mutations, don’t hesitate to talk with your doctor. He or she may perform a risk assessment or order genetic testing.

Tools for assessing your breast cancer risk

There are tools to calculate your risk of developing breast cancer. Most take into account your age, ethnicity, family history and other criteria, such as weight, previous biopsies, age of first menstruation or first pregnancy.


How can I lower my risk of breast cancer?

Many of the risk factors for developing breast cancer are related to our lifestyle habits. This means we can take action to improve our lifestyle and reduce our risk. Healthy lifestyle habits are the best way to lower our risk of developing all diseases. For instance, a balanced diet, enough physical activity and sufficient sleep are the pillars of a healthy life.

The Quebec Breast Cancer Foundation encourages women to adopt healthy lifestyle habits by incorporating several simple actions into their daily lives.

  1. Observe your breasts. Know your body and watch for persistent and recent changes.
  2. Get a mammogram. Have a mammogram every two years, from age 50 to 69, or as recommended by your doctor.
  3. Evaluate your preventive surgery options if you have increased chances of heredity cancer. If there is a history of breast cancer in your family, talk to your doctor. A high-risk woman can significantly reduce her risk by having preventive surgery (e.g. preventive mastectomy, ovarian ablation). 
  4. Maintain a healthy body weight. Watch your weight. Obesity increases the risk of breast cancer, especially in postmenopausal women who have never used hormone replacement therapy.
  5. Get enough exercise. Running, walking, being active: more than four hours a week of high-intensity physical activity reduces your risk. The effect of exercise on breast cancer risk may be greater in premenopausal women with normal or low body weight. 
  6. Moderate your alcohol consumption. The level of risk increases with the amount of alcohol you consume.

Discover our My Active Health exercise program

What screening tests are available and how often should they be done?

Regardless of whether you are at risk, it is strongly recommended you get regular breast cancer screening. It is important that, in the event that cancer cells develop, they be detected as early as possible. The earlier breast cancer is discovered, the better the chances of a cure.

The Quebec Breast Cancer Screening Program (QBCSP) recommends that all Quebec women between the ages of 50 and 69 have a screening mammogram every two years. In Quebec, mammograms are the only recommended breast cancer screening exam. Also, get to know your breasts by observing them regularly so you can detect any change in their appearance.

  • Breast self-examination is no longer recommended by the QBCSP because it is not considered an effective means of screening. Data has shown that the past recommendation did not reduce breast cancer mortality and may have caused unnecessary examinations and worry. However, be sure to stay alert and report any changes in your breasts to your doctor. 
  • Previously, it was recommended to get regular clinical breast exams by your doctor. However, since clinical breast examination has not decreased mortality from breast cancer, this test is no longer among QBCSP’s recommendations. But be careful to tell your doctor about your concerns and any changes you observe. He or she will proceed with a clinical examination if necessary.