The benefits and risks of hormone replacement therapy (HRT) are complex and confusing. HRT, used to relieve symptoms of menopause, was the subject of the famous Women's Health initiative, a large-scale study that was halted in 2002 when HRT was shown to increase a woman's risk-and delay diagnosis-of breast cancer. HRT has been shown in some studies, however, to reduce a woman's risk for colorectal cancer (CRC).

CRC is the third leading cause of cancer death in women in the United States, although it's highly treatable when caught early. In early studies, older women who used HRT had a 28 percent decrease in risk of developing this cancer. However, researchers were quick to point out that CRC prevention was not a reason to start or continue HRT.

In the Women's Health Initiative, researchers found that women taking a combination of estrogen and progesterone HRT had a 40 percent reduction in colon cancer risk. When the women stopped HRT, the risk reduction benefit stopped as well. Interestingly, HRT users who did develop colon cancer had a more advanced case at time of diagnoses. More than half of the women (58 percent) taking HRT had vaginal bleeding in the first year of the study, compared to only seven percent who were not taking HRT. Researchers believe this symptom prompted physicians to evaluate women for endometrial cancer, essentially delaying a colon cancer diagnosis until the cancer reached a more advanced stage.

A more recent study of the connection between HRT and colon cancer found that estrogens do provide some protection for woman against developing CRC cancer, and that HRT is associated with an increase in survival rate in women who developed CRC. Postmenopausal women, and women who had multiple pregnancies, both had reduced risks for colon cancer, further supporting the CRC protective factor of estrogen. When researchers analyzed the results from multiple HRT studies, they found that women who previously took HRT had a 20 percent reduction in their relative risk for CRC. In women currently using HRT, this increased to 34 percent.

The bottom line

Until we know more, medical experts recommend that women who choose HRT use the lowest dose possible for the shortest amount of time. HRT should not be considered a preventative strategy for colon or rectal cancer. Furthermore, women should be screened for colon cancer starting at age 50 (earlier if they have additional risk factors), and doctors should be diligent about colon cancer screening among postmenopausal women who are using HRT.