Breast cancer risk factors

Being born a woman is in itself a risk factor for breast cancer, since more than 99% of cases develop in women. The disease appears in men in about 1% of cases, and they’re often over 60 years old. Learn more about male breast cancer here.

The risk of breast cancer increases with age. The longer a woman lives, the greater the likelihood that she will one day develop the disease. This type of cancer is more common among women between the ages of 50 and 69; however, nearly 15% of cases occur in women under 50. About 20% of cases are diagnosed in women over 70.

The risk of breast cancer increases with age. The longer a woman lives, the greater the likelihood that she will one day develop the disease. This type of cancer is more common among women between the ages of 50 and 69; however, nearly 15% of cases occur in women under 50. About 20% of cases are diagnosed in women over 70.

Women with dense breasts are more likely to develop breast cancer. While breast density decreases with age and after the menopause, it can be affected by lifestyle; for example, use of hormone replacement therapy, a late first pregnancy, no pregnancy, and alcohol consumption can all increase breast density.

Having received radiation or ionizing rays for medical treatment is a risk factor for breast cancer. The risk is higher if the treatment was administered with chemotherapy during puberty or before the age of 15.

Women with atypical hyperplasia, a benign (non-cancerous) condition in which there are more abnormal (atypical) cells in the breast tissue, are at greater risk of developing breast cancer.

People who have already had breast cancer have at greater risk of developing it again, either in the same breast or the other. People who’ve had ovarian cancer may also be at higher risk of developing breast cancer.

The risk increases if one or more family members, on either the mother’s or father’s side, have had breast or ovarian cancer, particularly if the cancer was diagnosed in a woman before menopause. In addition, a woman’s risk increases with the number of first-degree relatives (father, mother, sister or daughter) who have had breast or ovarian cancer.

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

• Two or more family members who have had breast or ovarian cancer.
• One family member who has had both breast and ovarian cancer.
• One male family member who has had breast cancer.

It’s important to note that most of those affected have no family history of the disease. Be aware: if there’s a history of breast cancer in your family, speak to your doctor.

Go here to view our educational videos on hereditary breast cancer.

If you are concerned about the risk of breast cancer linked to a personal or family history, don’t hesitate to speak to your doctor. They can assess your personal risk of breast cancer and refer you to a genetic counsellor if they feel it’s necessary.

The genes we inherit can mutate over generations, increasing the risk of developing cancer. Maternal and paternal genetic mutations have a 50% probability of being passed on to children.

Around 10% of breast cancer cases are attributable to a known genetic mutation. Go here to find out more about genetics and breast cancer.

The genes that are most known to be associated with breast cancer are BRCA1 and BRCA2. Mutations in these genes make some women more likely to develop the disease.

Mutations in other genes (ATM, CDH1, CHEK2, BARD1, MRE11A, MSH6, NBN, PALB2, PMS2, RAD50, RAD51C, RAD51D, NF1, or SEC23B) have also been associated with a higher risk of breast cancer.

Certain other rare inherited genetic disorders also increase the risk of breast cancer: Li-Fraumeni syndrome, ataxia-telangiectasia, PTEN hamartoma tumour syndrome (PTHS) and Peutz-Jeghers syndrome.

Major studies are being done to better characterize which mutations, or combinations of them, might increase the risk of developing breast cancer. Eventually, it may be possible to determine risk levels based on genetic profile, enabling individual assessment and personalized screening strategies based on that level.

See the website of the PERSPECTIVE study, funded by the Quebec Breast Cancer Foundation (in French only).

If you are a carrier of a genetic mutation, find out more about the National Comprehensive Cancer Network (NCCN) risk-management guidelines for people with a hereditary risk for cancer here.

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

The onset of menstruation at a young age, before the age of 12, lengthens the duration of exposure to estrogen and other hormones and therefore increases the risk of breast cancer.

The later menopause occurs, for example after age 55, the longer a woman is exposed to estrogen during her lifetime, and this increases the risk for breast cancer.

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

While HRT generally succeeds in relieving women of the undesirable effects of menopause, it is believed to increase the risk of breast cancer since it contains estrogen, a hormone linked to the disease. Studies have shown that the risk of developing breast cancer increases after using hormone replacement therapy for five years, and even more so if it also contains progestin.

The increased risk seems to disappear a few years after the treatment ends; however, many researchers believe that the risks of long-term use of HRT in combination with progestin outweigh the benefits of this treatment.

Women struggling with severe effects of menopause therefore need to decide, with the help of their doctor, what is the best choice for their health: to take HRT or not, based the severity of undesirable symptoms and their personal risk factors for breast cancer.

Regardless of their choice, it is highly recommended that pre- and post-menopausal women discuss their personal risk for breast cancer with a doctor, observe their chest and breasts, and follow screening recommendations.

Contraceptives that contain estrogen and progesterone also slightly increase the risk of breast cancer, especially for women who have used them for 10 years or more. This said, the increased risk ceases once the use of hormonal contraceptives is stopped.

Taking estrogen and progesterone as part of gender-affirming therapy is also associated with an increased risk of breast cancer. For more information, see breast cancer in 2SLGBTQIA+ people.

During pregnancy, a woman’s breast cells temporarily stop being exposed to circulating estrogen; therefore, the more pregnancies a woman has, the less she is exposed to this hormone linked to breast cancer, as opposed to women who have not had any children or have not carried any pregnancies to term.

In addition, women whose first pregnancy is after the age of 30 have a slightly higher risk than women whose first full-term pregnancy is at a younger age.

Lastly, according to several studies, breastfeeding is considered to be a protective factor against breast cancer.

Alcohol consumption increases the risk of breast cancer, regardless of the type consumed. There is no safe amount of alcohol, and the risk increases proportionally with the amount you drink.

There are two possible reasons to explain the link between alcohol consumption and an increased risk of breast cancer:

• Alcohol may increase levels of estrogen, a hormone associated with breast cancer.
• Alcohol may also reduce essential nutrients that protect against cell damage, such as folic acid, a type of vitamin B, and vitamins A and C.

It is therefore advisable to limit your alcohol consumption. The less you drink, the more you limit your risk. To learn more about this topic, see Canada’s Guidance on Alcohol and Health and the blog post Alcohol and breast cancer.

Research indicates that not exercising is a risk factor for breast cancer. Conversely, studies show a link between regular physical activity and a reduced risk of developing the disease. Doing 150 minutes of moderate-to-high intensity physical activity a week reduces the risk of developing breast cancer by 25%. At the same time, it’s also important to limit sedentary behaviour (time spent sitting or lying down).

Being overweight or obese¹ increases the risk of developing breast cancer in postmenopausal women. After menopause, fatty tissue produces a small amount of estrogen, and an increase in this hormone is associated with breast cancer.

Recent studies have shown that active smoking increases the risk of breast cancer. There’s also a link between exposure to second-hand smoke and breast cancer, but the evidence is most convincing in young or premenopausal women who have never smoked.