Breast Cancer Hormones

Since 2002, the potential side effects of hormone replacement therapy (HRT) have been called into question, namely due to its possible role in causing a number of serious disorders and conditions. HRT, which involves taking estrogen and progesterone supplements, had been prescribed throughout the years to alleviate unwanted side effects of menopause.

However, doctors began to notice that HRT seemed to promote the development of breast cancer, heart disease and stroke. This observation led researchers to further investigate the link between hormones and breast cancer.

Hormone Receptor Positive Breast Cancer

“Hormone receptor positive breast cancer” refers to a type of breast cancer that arises and grows due to the presence of estrogen and/or progesterone receptors on cancerous cells in the breast. Hormone receptors are highly refined proteins on a cell’s surface that are designed to interact and bind with specific hormones. In cases of hormone receptor positive (HR ) breast cancer, tumors grow because their HR cells are getting the estrogen and progesterone they need to reproduce. About 75 percent of all breast cancer cases are hormone receptor positive (Reuters Health, 2010).

As a result, women who have hormone receptor positive cells shouldn’t be prescribed hormone replacement therapy to treat menopause symptoms, as these women are at a particularly high risk of developing breast cancer. HRT will introduce more hormones into their systems, feeding the HR cells and promoting the growth of cancerous cells in the breast.

Long-Term Estrogen Exposure and Breast Cancer Risk

The risk of developing breast cancer increases significantly as women age, and this is most true for women who have been exposed to estrogen for a greater than normal amount of time. For instance, women who began to menstruate before the age of 12 or who began menopause after the age of 55 will have had higher than average estrogen exposure throughout their lives. Women who give birth after the age of 35 similarly increase their risk (National Cancer Institute, 2008).

Tamoxifen®, Aromatase Inhibitors and Breast Cancer

Tamoxifen® is an antiestrogen drug that binds to hormone receptor positive cells to prevent them from interacting with estrogen. While Tamoxifen® has been proven effective in preventing breast cancer in HR patients, it has also been linked to the development of endometrial (uterine) cancer (American Cancer Society, 2009). Another downside to Tamoxifen® is the fact that it isn’t effective in all HR patients. Some who have taken Tamoxifen® still develop breast cancer.

Another class of drugs, called “aromatase inhibitors,” is used to treat early and advanced HR breast cancer in post-menopausal women. Aromatase inhibitors block an enzyme that produces small amounts of estrogen. These drugs do not work in pre-menopausal women because they do not stop the ovaries from producing estrogen.


The American Cancer Society. (2009). Breast cancer facts and figures 2009-2010. Retrieved on October 20, 2010 from

National Cancer Institute. (2008). Pregnancy and breast cancer risk. Retrieved October 20, 2010 from

Breast Cancer Advice. (2006). Aging of breast tissue. Retrieved October 20, 2010 from

Pruthi, S. (2009). Mammogram guidelines: What’s changed? Retrieved October 20, 2010 from

Reuters Health. (2010). Breast cancer rates fell with hormone therapy drop. Retrieved on November 2, 2010, from