​Life-long exposure to the body’s natural hormones—estrogen and progesterone —is essential for the normal growth and development of a woman's breasts and reproductive system. However, these natural hormones also play a role in increasing our breast cancer risk. 

Synthetic hormones can also increase a woman’s risk of developing breast cancer and they are our focus here. Synthetic hormones are made in a laboratory and form part of the medications we choose to take as women at different life stages: to prevent or enable pregnancy or to manage the symptoms of menopause.

Factors that increase a woman's exposure to synthetic hormones include her use of birth control pills, fertility treatment to become pregnant and hormone replacement therapy during menopause.

Oral contraceptives (the Pill)

Oral contraceptives (also called the birth control pill or “the Pill”) have both benefits and limitations that you should know about in order to make an informed decision about whether they are right for your reproductive health and overall health as well as your lifestyle.

The Pill was developed to prevent unplanned pregnancy, but it is also prescribed for other uses, such as regulating the period and for other conditions.

The combined Pill

Using birth control pills that contain both estrogen and progesterone (combination pills) exposes you to a low increase in the risk of developing breast cancer compared to women who do not take them. 

The good news is that 10 years after stopping the combined Pill, your increased risk for breast cancer disappears, and the chance of developing breast cancer becomes similar to that of a woman with your risk factors who has never taken the Pill. There is also evidence that the Pill may decrease the risk for developing ovarian and endometrial cancers. 

To make an informed decision about what is right for you, the Canadian Breast Cancer Foundation encourages you to learn about the benefits and limitations of using oral contraceptives for your lifestyle as well as your overall health and well-being. To inform your decision,we also encourage you to speak to a health care provider about your medical history, your lifestyle, the benefits and risks of the Pill, and alternatives to it.

Fertility treatment

Fertility treatment is also known as IVF, short for in-vitro fertilization. The aim of fertility treatment is to help a woman become pregnant. The process unites an egg and sperm (or several) in the laboratory (in vitro). Embryos are then transferred to the woman’s womb.  

IVF often uses fertility drugs to stimulate ovulation. These drugs increase the level of female hormones such as estrogen in the woman’s body, and some concerns have been raised that this may increase the risk of breast cancer. 

IVF is still a relatively new procedure, and only a very small number of studies have looked at the effect of IVF on breast cancer risk.  Current research findings are inconclusive about the link between IVF and increased breast cancer risk. More research is needed to assess the long-term breast cancer risk of fertility treatment.    

To make an informed decision, the Canadian Breast Cancer Foundation encourages you to speak to a health care provider about the benefits and limitations of fertility treatment. You may wish to discuss your medical history, your lifestyle, the short and longer term benefits and risks of fertility treatment and alternatives to it.

Menopause and HRT

Conclusive research has linked the use of combined hormone replacement therapy (HRT) to a moderate increase in the risk of breast cancer.  In Canada, a 2010 study reported a direct link between a decline in the incidence of breast cancer in postmenopausal women as their use of combined HRT decreased. The use of combined HRT declined significantly in response to findings from the Women’s Health Initiative in 2001, which found an increase in the risk of breast cancer, heart disease and other health risks in women taking combined HRT.  

Some women going through menopause choose to take HRT to relieve symptoms such as hot flashes and vaginal dryness, or to decrease the risk of certain conditions such as osteoporosis. 

HRT may be effective at relieving these symptoms because it offsets the changing levels of estrogen and progesterone that happen naturally when menopause begins. Women experience menopausal symptoms to various degrees from mild to severe. 

If you are considering HRT, you should be aware that the combined therapy is associated with an increased risk of breast cancer and other risks to your health. Health Canada suggests that HRT should be used only if your menopausal symptoms are severe.

If you are already taking HRT, your risk of breast cancer is increased while you are taking HRT and continues to increase the longer you continue to use it.  However, once you stop taking HRT, your risk of breast cancer begins to decrease. Some research suggests that five years after stopping HRT, the risk of breast cancer may be much the same as women who have never used HRT.

Coping with Menopause

To make an informed choice about whether HRT is right for you, the Canadian Breast Cancer Foundation encourages you to learn about the benefits and limitations of different types and dosages of HRT. To inform your decision, we also encourage you to speak with a health care provider about HRT as well as alternative ways of coping with your menopausal and postmenopausal symptoms. This may include complementary medications and lifestyle changes, such as decreasing your intake of alcohol, not smoking, increasing your level of physical activity and eating a healthier and well-balanced diet. 

Established risk factors

Sources

Allan Jensen et al. (2007). Risk of Breast Cancer After Exposure to Fertility Drugs: Results for a large Danish cohort study. In Cancer Epidemiology Biomarkers and Prevention 16 (7). Accessed July 31, 2011.

Breakthrough Breast Cancer (UK). Breast Cancer Risk: the Facts – The Pill. Accessed July 31, 2011.

Health Canada. Benefits and Risks of Hormone Replacement Therapy. Accessed July 31, 2011.

National Cancer Institute (US). Menopausal Hormone Replacement Therapy Use and Cancer. Accessed July 31, 2011.

Mayor. S. (2010). Incidence of breast cancer falls with less HRT use, Canadian study confirms.  In British Medical Journal. BMJ 2010, 341: c5307. Accessed July 31, 2011.