Tamoxifen is a medication approved by the US Food and Drug Administration to help reduce breast cancer risk. Another medication, raloxifene—currently used to prevent and treat osteoporosis —has shown promise in reducing breast cancer risk in postmenopausal women with osteoporosis. Both medications are so-called selective estrogen receptor modulators (SERMS), which act like estrogen on certain tissues (eg, bones) and block estrogen on other tissues (eg, breast cancer cells).

A new study that will be published in the June 21, 2006 issue of the Journal of the American Medical Association found that raloxifene is as effective as tamoxifen in reducing the risk of invasive breast cancer. Both medications, however, were associated with a specific set of risks and benefits.

About the Study

This study included 19,747 postmenopausal women who were randomly assigned to receive either tamoxifen (20 milligrams per day) or raloxifene (60 milligrams per day) for up to five years. The women were at increased risk of developing invasive breast cancer, in most cases due to a family history of breast cancer, or a personal history of noninvasive breast cancer or abnormal breast biopsy. The researchers evaluated the participants every six months to determine if they had developed breast cancer, other cancers, cardiovascular problems, or bone fractures.

During the study, 331 participants developed invasive breast cancer. There was no difference between tamoxifen and raloxifene in reducing the risk of invasive breast cancer. Blood clots (eg, in the lungs or deep veins) occurred 30% less often in the raloxifene group than in the tamoxifen group. The risk of developing cataracts and having cataract surgery was lower in the raloxifene group as well.

There were fewer noninvasive breast cancers and more uterine cancers in the tamoxifen group, but these findings did not reach statistical significance. There was no significant difference between the groups in the risk of developing other cancers, heart disease, stroke , or fractures.

How Does This Affect You?

These findings suggest that raloxifene is as effective as tamoxifen in reducing the risk of breast cancer. In another study in the same journal issue, researchers evaluated a subset of 1,983 participants and found no difference in physical or mental health, although the tamoxifen group reported better sexual function.

Reports of symptom severity were low overall, but women in the tamoxifen group were more likely to report gynecological problems, vasomotor symptoms (eg, night sweats, hot flashes), leg cramps, and bladder control problems, whereas women in the raloxifene group reported more musculoskeletal problems, pain during sexual intercourse, and weight gain.

If you think you are at increased risk of breast cancer, talk to your doctor about how you can reduce your risk. In addition to medications, breast cancer prevention strategies include mastectomy surgery before breast cancer occurs and/or participating in an intensive screening program to reduce the risk of mortality. If you choose the medication route, it is clear that tamoxifen and raloxifene, while generally well tolerated, each has its own unique set of adverse effects to consider when deciding which one is right for you.