Breast cancer

The following have been linked with an increased risk of breast cancer in women, but more research is needed to know for sure that they are risks.

Smoking tobacco may increase the risk of breast cancer in both premenopausal and post-menopausal women.

Second-hand smoke may increase the risk of breast cancer in younger, premenopausal women who have never smoked.

Learn more about how to live smoke-free.

If you weighed more than 4 kilograms when you were born you may have an increased risk of developing breast cancer before menopause. This may be related to growth factors, such as tall adult height, that are linked to a higher risk of breast cancer.

If you work shifts (working outside the hours of the normal workday), especially night shifts, you may have a slightly higher risk of developing breast cancer. Researchers think that night work, and being exposed to artificial light, lowers the amount of melatonin in the body. In women, melatonin lowers the amount of estrogen in the body, and it may slow the growth of breast cancer cells.

Most non-cancerous (benign) breast conditions do not increase your risk of developing breast cancer. But there may be a relationship between some non-cancerous breast conditions and a family history of breast cancer. Some non-cancerous breast conditions may slightly increase your risk of breast cancer if they are linked with a greater number (overgrowth) of cells. Non-cancerous breast conditions that may increase the risk for breast cancer include:

• fibrocystic breast changes
• hyperplasia
• complex fibroadenoma
• sclerosing adenosis
• papillomatosis
• radial scar

There have been a few reports of women with breast implants (silcone and saline) developing an extremely rare type of breast cancer called squamous cell carcinoma.

Health Canada is monitoring reports of this type of cancer in women with breast implants.

Diethystilbestrol (DES) is a manufactured form of the hormone estrogen. From about 1940 to 1971, DES was used to prevent miscarriage and other complications of pregnancy.

Children of women who were given DES while pregnant with them may have a higher risk of developing breast cancer.

To make the decisions that are right for you, ask your healthcare team questions about risks. Learn how cancer can be prevented and what you can do to reduce your risk.

Some people can have a higher than average risk for breast cancer. Talk to your doctor about your risk. If you are at higher than average risk, you may need to visit your doctor more often to check for breast cancer. Your doctor will recommend which tests you should have and how often you should have them.

If you have a BRCA1 and BRCA2 mutation, your doctor may talk to you about the benefits and risks of following strategies that may reduce your risk of breast cancer.

Chemoprevention is using drugs to reduce the risk of cancer. Tamoxifen is a type of anti-estrogen drug called an estrogen receptor blocker. It lowers the risk of developing breast cancer by blocking the effects of estrogen in breast tissue.

People with BRCA1 mutations are more likely to have a type of breast cancer (called estrogen–receptor positive breast cancer) that responds to tamoxifen. People with BRCA2 mutations are less likely to have estrogen–receptor positive breast cancer, but tamoxifen can still reduce risk.

Tamoxifen very slightly increases the risk for uterine cancer, blood clots and stroke. Most of the time, the benefits of taking tamoxifen outweigh the risks.

A prophylactic mastectomy is having one or both breasts removed by surgery before cancer develops in them. This surgery may be an option for some people if they know they have a BRCA mutation or if they have already had cancer in one breast. A prophylactic mastectomy reduces the risk of breast cancer by about 90% in high-risk people. Find out more about surgery for breast cancer.

A prophylactic oophorectomy is having the ovaries removed before cancer develops. The ovaries are the body's main source of estrogen, so removing them lowers the level of estrogen in the body. This can lower the risk for breast cancer in people with BRCA mutations. It can also lower the risk of ovarian cancer. Find out more about surgery for ovarian cancer.