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.

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.