Breast cancer is a multifactorial disease: several factors can increase the risk of its occurrence. Some are independent of lifestyles, while others are closely related to behavior and environment. There are thus 3 main types of risk factors:

• genetic factors
• hormonal and reproductive factors
• environmental and behavioral factors

Risk factors unrelated to the environment

Some women have a higher risk of developing breast cancer, regardless of their lifestyle.

• Age

Besides gender (breast cancer affects 99% of women), age is the main risk factor for breast cancer. Although it can affect all women, the risk of developing breast cancer increases with age. Young women are thus very little affected by this type of cancer.

Most breast cancer develops in women aged 50 to 69 (around 60 on average). Almost a third is diagnosed after 69 years. This is why it is recommended that all women between the ages of 50 and 74 get tested, using a mammogram. Entirely covered by Health Insurance, this examination must be carried out every two years.

• Personal history of illness and hormonal factors

The risk of developing breast cancer is also linked to each woman’s personal medical history. A patient who has had this type of cancer in the past is at particularly high risk of developing a new one. There is also a risk of recurrence in the breast already treated. These “at risk” women must therefore be monitored regularly.

Women who have suffered from a benign breast condition (a condition associated with the overgrowth of cells in the breast tissue, such as hyperplasia) are also at greater risk of developing breast cancer. These patients should be closely monitored by their doctor. Some exams are done on a regular basis (a clinical breast exam or a mammogram).

Exposure of the chest to certain ionizing radiations (medical radiations, for example) is also one of the factors that can increase the risk of developing breast cancer. The increased risk depends on the age of the woman and the radiation dose received. This applies to women who have been treated with radiation therapy for another type of cancer, as well as women who have had their lungs X-rayed in their childhood (for example, to screen for tuberculosis).

• Endogenous hormonal factors

Certain endogenous hormonal factors can also increase the risk of developing breast cancer. Thus, the onset of menstruation at an early age (before 12) or late menopause (after 50 years) increases this risk (due to early and prolonged exposure to ovarian hormones). Estrogens have an effect on the cells of the breast. The longer the total duration of exposure to estrogen in the blood, the greater the risk of developing breast cancer.

The risk of developing this breast cancer also increases with the level of density of breast tissue. Having a large breast can therefore be a risk factor for breast cancer. The denser the breasts are on a mammogram, the higher the risk.

Family history of cancer and genetic predisposition

Women with a family history of cancers, including breast cancer, have a higher risk of developing breast cancer in turn. This predisposition may be due to the fact that people of the same family share certain lifestyle habits or to a genetic and hereditary anomaly, transmitted from ancestors to descendants.

According to studies, the risk of developing breast cancer increases slightly when the person who has already suffered from cancer is a second-degree relative (grandmother, aunt, niece). On the other hand, if it is a first-degree relative (mother, sister, daughter), this risk increases significantly (especially if breast cancer was diagnosed in a young patient or in both breasts, before menopause).

Between 5 and 10% of breast cancers are due to a genetic mutation. These mutations, which promote the development of this type of cancer, usually involve genes called BRCA1 and BRCA2 (for BReast Cnncer 1 and 2). A woman who carries a mutation in one of these genes will not necessarily have breast cancer. However, this mutation increases the risk of developing one (at a young age, in both breasts, or ovarian cancer). When the mutation is discovered, special and regular care is offered to the patient.

Other genetic mutations can play a role in the development of breast cancer. They relate to genes involved in DNA repair or stopping cell multiplication in the event of injury: the T53, CHEK2, ATM, PTEN, STK11 genes.

Environmental risk factors

Several behavioral and environmental factors can be responsible for the development of breast cancer in young women, as in older women.

• The consumption of tobacco and alcohol

Smoking and drinking too much alcohol (from an average drink of one drink per day) increases the risk of developing several types of cancer, including breast cancer. Passive smoking is also one of the risk factors. Tobacco smoke contains several carcinogenic substances. Alcohol can increase the production of estrogen in the blood.

In general, a healthy and balanced diet (neither too fatty, nor too sweet, nor too salty) allows you to put all the chances on your side to stay in good health.

• Lack of physical activity and overweight

Overweight and obesity are among the main behavioral factors that increase the risk of developing breast cancer in postmenopausal women. A person is deemed overweight when his or her BMI (Body Mass Index) is between 25 and 29.9. Obesity affects people with a BMI of 30 or more. Fat tissue produces small amounts of estrogen, hormones that are involved in the onset and development of breast cancer.

Conversely, participating in a physical or sports activity on a regular basis reduces the risk of developing breast cancer after menopause. The ideal is to practice sustained physical activity throughout your life.

• Hormonal treatments and reproduction

Women who take the contraceptive pill continuously for a long time are more likely to develop breast cancer. However, this risk disappears when the contraceptive treatment is stopped (after 10 years of stopping, no increased risk is noted). But several studies also show that taking the pill lowers the risk of developing ovarian cancer, especially in women whose BRCA1 and BRCA2 genes carry mutations.

On the other hand, when given continuously over a long period of time, taking HRT (Hormone Replacement Therapy) during menopause also increases the risk of developing this type of cancer. Prescribed to compensate for the decrease in the level of ovarian hormones, HRT for menopause indeed contains estrogen and progesterone. However, these two hormones play an important role in the development of this type of cancer.

The absence of a completed pregnancy and late pregnancies also influence the development of breast cancer. This is because pregnancy reduces the number of a woman’s menstrual cycles. It also temporarily limits the exposure of breast cells to estrogen. Women who carried at least one pregnancy to term before their 30s have a reduced risk of developing breast cancer. Multiparity (having given birth several times) and prolonged breastfeeding also have a protective effect against breast cancer.