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Exposure To Synthetic Hormones

Life-long exposure to the body’s natural hormonesHormone:
A natural substance released into the body by the endocrine glands, such as the thyroid, adrenal gland or ovaries.
A female sex hormone that is produced mainly in the ovaries. A woman’s levels of estrogen fluctuate throughout her life. Estrogen has been linked to the development of breast cancer and may promote the growth of cancer cells.
and progesteroneProgesterone:
A female sex hormone released by the ovaries during the woman’s menstrual cycle to prepare the uterus for pregnancy and stimulate milk production in the breast. It is also one of the synthetic hormones used in hormone replacement therapy.
—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 menopauseMenopause:
A natural part of a woman's aging process, when the ovaries start to make less estrogen and progesterone and the menstrual periods stop. This change typically occurs between the late 40s and mid-to-late 50s.

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 therapyHormone replacement therapy (HRT):
Is a hormone treatment intended for women who have reached the age of menopause, to reduce its symptoms. It involves taking small doses of estrogen and progesterone (combined) or just estrogen alone.
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) may cause a slight increase in your risk of developing breast cancer compared to women who do not take them. Longer term use of the Pill (5 years or more) also increases the risk of cervicalCervix:
The lower, narrow part of the uterus that connects to the vagina.

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 factorsRisk factor:
Anything that increases a person’s chance of developing a disease, such as cancer.
who has never taken the Pill. There is also evidence that the Pill may decrease the risk for developing ovarianOvary:
A female reproductive organ in which ova or eggs are produced. The ovaries also produce the female hormones estrogen and progesterone.
and endometrialEndometrium:
The tissue that lines the inside of the uterus. It thickens every menstrual cycle and is shed during menstruation if pregnancy does not occur.

Although most research examining the effects of hormonal birth control on breast cancer risk has looked at the birth control pill, other forms of combined hormonal birth control (containing both estrogen and progesterone), such as the patch or the vaginal ring, may carry the same benefits and risks as the Pill.

To make an informed decision about what is right for you, Canadian Breast Cancer Foundation encourages you to learn about the benefits and limitations of using hormonal birth control methods 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 combined hormonal contraceptives, and alternatives to it.

Fertility Treatment

Fertility treatments are used to help a woman become pregnant. There are different types of fertility treatments, ranging from medications (e.g., Clomid), to procedures such as in-vitro fertilization (IVF). IVF is a process that unites an egg and sperm (or several) in the laboratory (in vitro). Embryos are then transferred to the woman’s womb. 

Most fertility treatments use drugs to stimulate ovulationOvulation:
The release of an egg from an ovary.
. These drugs briefly 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.

Current research findings related to fertility treatments and increased breast cancer risk are still inconclusive, with some results suggesting a link between fertility treatments and breast cancer risk and others finding no relationship. More research is needed to assess the long-term breast cancer risk of fertility treatment.   

If you are considering fertility treatment and are concerned about a possible increase in your risk of developing breast cancer, speak to a health care provider about the benefits and limitations of fertility treatment to help you make an informed decision about what is right for you. 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.  The use of combined HRT declined significantly in response to findings from the Women’s Health Initiative in 2002 which found an increase in the risk of breast cancer, heart disease and other health risks in women taking combined HRT.  In Canada, a 2010 study reported a decline in the incidenceIncidence (rate):
The number of newly diagnosed cases of a disease during a specific time period. Incidence helps us to understand the risk of developing that disease.
of breast cancer as the use of combined HRT among women aged 50-69 decreased.

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 osteoporosisOsteoporosis:
A condition where the amount and quality of bone in the body are reduced. It causes bones to become weak and brittle, making them more prone to fractures (broken bones).

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. Using HRT can also make your breasts more denseDense breasts (breast density):
Dense breasts have less fat and more glandular and connective tissue. A woman’s breast density depends on her age and genetic factors. Breast density is a risk factor for breast cancer. Having “dense breasts” is a clinical diagnosis that can only be assessed by mammography.
, which can make it more difficult to detect breast cancers by mammogram.  Wherever it is available, ask to be screened using digital mammographyDigital mammography:
A low-dose X-ray similar to screen-film mammography, equipped with a digital receptor and a computer instead of film.
, as this newer technology is better at detecting breast cancer in women with dense breasts.

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 5 years after stopping HRT, the risk of breast cancer may be much the same as women who have never used HRT.

Bio-Identical Hormone Therapy (“Natural Hormone Therapy”)

You may have heard about or considered using bio-identical hormones during menopause. “Bio-identical” is a term used to describe hormones that have an identical chemical structure to the hormones produced by your body, and usually refers specifically to estrogen and progesterone. They are often marketed as being “natural” because they can be produced from plant sources, but natural doesn’t always mean safe. At this time, there is no evidence that suggests that bio-identical hormones are safer for treating the symptoms of menopause than synthetic forms of estrogen and progesterone used in HRT.

When faced with a lack of scientific evidence, we have options. Canadian Breast Cancer Foundation supports the use of a precautionary approachPrecautionary principle (precautionary approach):
An approach to preventing harm to human health and the environment when the scientific evidence is not conclusive. When we face scientific uncertainty, we have options and we can act. If we think there is potential for harm, we can choose to take preventive action now – this is what’s known as the precautionary principle.
– erring on the side of caution and taking preventive action until more information becomes available.

Coping with Menopause

To make an informed choice about whether HRT is right for you, 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.


Allan Jensen et al. (2007). Risk of Breast Cancer After Exposure to Fertility Drugs: Results for a large Danish cohort study. Cancer Epidemiology Biomarkers and Prevention 16 (7), 1400-1407.

American Cancer Society. Menopausal Hormone Therapy and Cancer Risk. Accessed February 23, 2014.

Breakthrough Breast Cancer. The pill and breast cancer risk. Accessed June 23, 2014.

De, P., Neutel, C.I., Olivotto, I., and Morrison, H. (2010). Breast cancer incidence and hormone replacement therapy in Canada. Journal of the National Cancer Institute, 102(19), 1489-1495.

Health Canada. Benefits and Risks of Hormone Replacement Therapy. Accessed June 23, 2014.

National Cancer Institute. Menopausal Hormone Replacement Therapy and Cancer. Accessed June 23, 2014.

National Cancer Institute. Oral Contraceptives and Cancer Risk. Accessed April 1, 2014.

Mayor, S. (2010). Incidence of breast cancer falls with less HRT use, Canadian study confirms. British Medical Journal, 341: c5307. Accessed June 23, 2014.