Hormone therapy and the risks of breast and endometrial cancers
Breast cancer
Your risk of developing breast cancer increases slowly as you age, especially after age 50. About 1 in every 9 women in Canada may get breast cancer during her lifetime.1 Taking estrogen with progestin (hormone replacement therapy, HRT) further increases that risk.2 Taking estrogen alone may slightly increase breast cancer risk. Large studies have shown either a slight risk increase or none at all.3, 4
These average increased breast cancer risks are relatively low for the general population of post-menopausal women. However, your personal risk that hormone therapy will stimulate cancerous cell growth may be significantly lower or higher, depending on your risk factors. For more information about breast cancer risk factors, see the topic Breast Cancer.
Endometrial cancer
In Canada, endometrial (uterine) cancer is the most common cancer of the lower female genital tract. About 1 woman in 50 (2%) will develop endometrial cancer in her lifetime.5 Women with an intact uterus who take estrogen therapy without progestin increase their risk of endometrial cancer. Adding progestin protects the uterus from this risk.
Weighing cancer risks for women who still have a uterus
- Taking only estrogen (estrogen replacement therapy, ERT) after menopause increases your risk of endometrial cancer.
- Taking progestin along with estrogen (HRT) eliminates endometrial cancer risk. (Estrogen-only therapy stimulates overgrowth of the uterine lining, which can become cancerous. Progestin regulates that growth.)
- Although adding progestin protects your uterus, it increases breast cancer risk. The British Million Women Study researchers have found that, among women ages 50 to 64, long-term (10-year) HRT after menopause causes more breast cancers than long-term estrogen replacement therapy (19 per 1,000 versus 5 per 1,000).3 American Women's Health Initiative researchers have similarly found that after 5.2 years of use, HRT causes 4 per 1,000 breast cancers. Their ERT data do not show breast cancer from ERT use. However, experts still take the ERT cancer risk seriously.6, 4
- Some experts have recently asserted that there may be no advantage to taking progestin with estrogen (to prevent endometrial cancer), because the addition of progestin increases breast cancer risk.
Unanswered questions about short-term and low-dose hormone therapy
Using hormone therapy for a short time just after menopause is hoped to be low-risk. Some studies have suggested that short-term use of hormone therapy (up to 4 years) may not increase breast cancer risk.5, 6 Ongoing study is needed to see how much lower-dose and shorter-term HRT and ERT reduce the risks of using long-term hormone replacement, including risks of breast and gynecological cancers, cardiovascular disease, and Alzheimer's disease.
Other treatments that do not appear to increase breast cancer risk are available for hot flashes, osteoporosis, and heart disease.
| Author: | Kathe Gallagher, MSW Carrie Henley | Last Updated: August 4, 2006 |
| Medical Review: | Joy Melnikow, MD, MPH - Family Medicine Tom Bailey, MD - Family Medicine Carla J. Herman, MD, MPH - Internal Medicine | |
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