Breast Cancer - Hormone Therapy And Disease: Menopause

Content provided by the Faculty of the Harvard Medical School

Breast cancer

Well before the WHI results, a number of studies suggested a link between hormone replacement therapy and breast cancer. Researchers have long known that estrogen promotes the rate of cell division in breast tissue. In addition, cell division in the breast surges in tandem with the highest levels of progesterone during the menstrual cycle. Doctors have observed that hormones cause dense breasts, and postmenopausal women with dense breasts have more cancers. Also, women with osteoporosis, thought to be associated with low estrogen, have less breast cancer than those with stronger bones. Progesterone tends to prevent cancer in the uterus, but it may stimulate it in the breast.

Additional early evidence for the link between breast cancer and hormone therapy came from the Nurses' Health Study, in which researchers followed 120,000 women over a period of several years. The women periodically filled out questionnaires about their diet, exercise, and medical histories, including hormone use. The researchers observed a 9% increase in breast cancer risk in women taking combined hormone therapy and a 3.3% increase in those taking estrogen alone. Risk increased the longer women took the hormones but returned to normal once they stopped.

Conflicting studies were also published. But the WHI results corroborated earlier findings, showing a 26% increased risk of breast cancer among combined hormone users. In addition, women who took hormones tended to have larger and more advanced cancers than those seen in the placebo users. Surprisingly, the findings from the E-Only arm of the study showed no increased risk of breast cancer, which lends further support to the idea that progestogen might be fueling the increased breast cancer risk.

Findings from a major study in the United Kingdom, the Million Women Study, support those of the WHI. Data from more than one million women showed that current users of combined estrogen and progestogen had a twofold higher risk of developing breast cancer, while the risk of women who took estrogen alone was 1.3 times higher. What's more, the risks were similar for all forms of the medication — oral, transdermal, or implanted — and for both continuous and cyclical patterns of use.

For many women, the risk of breast cancer is one of the most important considerations in deciding whether to take hormone therapy. Risk assessment models are available through your physician or on the National Cancer Institute Web site (see "Resources"). You will have to weigh your risk profile — such as if you have a family history of breast cancer — with the severity of your menopausal symptoms to arrive at an informed decision. So far, doctors don't fully understand how combined hormone therapy's risk of breast cancer interacts with a woman's other risk factors.

Last updated:	August 13, 2007