While raloxifene and tamoxifen are similarly effective in reducing breast cancer risk, raloxifene also appears to lower the risk of developing endometrial cancer, researchers report in the September 1st issue of the Journal of Clinical Oncology.

“These data are important,” lead investigator Dr. Angela DeMichele told Reuters Health, “because they suggest a critical difference between tamoxifen and raloxifene that could help physicians in tailoring therapy to the patient.” She added, “A randomized clinical trial has shown that the drugs are roughly equivalent in terms of their ability to prevent breast cancer.”

Raloxifene and tamoxifen are two drug used to reduce the risk of invasive breast cancer in high-risk women by blocking the effects of estrogen on breast tissue. Tamoxifen is also used as a type of maintenance therapy for women who have already been treated for early breast cancer with surgery, radiation, and/or chemotherapy to reduce the risk of recurrence. Raloxifene is also used to treat osteoporosis.

To examine the effect of raloxifene and tamoxifen on endometrial cancer risk, DeMichele of the University of Pennsylvania, Philadelphia, and colleagues examined data on 547 women who were diagnosed with cancer of the endometrium, t-al cancer and 1410 controls. The endometrium is the lining of the uterus.

Some 3.3 percent of the cancer patients had taken raloxifene compared to 6.6 percent of the controls. Corresponding proportions for tamoxifen were 6.2 percent and 2.4 percent.

After adjusting the data for the effects of other risk factors, the risk of endometrial cancer in raloxifene users was half that of nonusers. Conversely, tamoxifen users were three times more likely to develop endometrial cancer than were raloxifene users.

Given the similarity in protection against breast cancer, continued DeMichele, “a secondary benefit, like a reduction in the risk of endometrial cancer, may be very important to patients who have not had a hysterectomy and are concerned about the increased risk of endometrial cancer with tamoxifen.”

SOURCE: Journal of Clinical Oncology, September 1, 2008.