Raloxifene after tamoxifen not beneficial

Taking raloxifene after five years of tamoxifen therapy does not prevent the recurrence of breast cancer in postmenopausal women and may actually stimulate growth of endometrial tumors, according to a Northwestern University study.

As described in an article in the Feb. 20 issue of the Journal of the National Cancer Institute, researchers Ruth M. O’Regan, M.D.,V. Craig Jordan and colleagues at Northwestern evaluated the effects on tumor growth of raloxifene after tamoxifen treatment in mouse models of breast and endometrial cancers.

They found that, after exposing breast and endometrial tumors in mice to combinations of estrogen, tamoxifen, raloxifene or no drug at all, raloxifene did not further prevent growth of breast tumors previously exposed to more than five years of tamoxifen. Moreover, raloxifene was less effective than tamoxifen in blocking the growth of endometrial tumors caused by low-dose estrogen.

Tamoxifen is a selective estrogen receptor modulator (SERM) that reduces breast cancer recurrence in women with early-stage breast cancer. However, studies show that the benefits of tamoxifen diminish after five years and that additional therapy with tamoxifen may significantly increase a woman’s risk for endometrial cancer.

Some studies have suggested that SERM raloxifene, which is used to prevent osteoporosis in postmenopausal women, may decrease risk for breast cancer without increasing risk for endometrial cancer.

Based on the results of their study, the Northwestern researchers now believe that in women completing five years of tamoxifen therapy, raloxifene may not further reduce the risk for breast cancer recurrence.

However, the ongoing Study of Tamoxifen and Raloxifene (STAR) study, a large randomized clinical trial that is comparing the effects of raloxifene and tamoxifen on the primary prevention of breast cancer and endometrial cancer in high-risk women, may provide more definitive answers on the utility of raloxifene following tamoxifen therapy.

O’Regan is an instructor in medicine at Northwestern University Medical School. Jordan is the Diana, Princess of Wales, Professor of Cancer Research; professor molecular pharmacology and biological chemistry at the Medical School; and director of Lynn Sage Breast Cancer Research Program at The Robert H. Lurie Comprehensive Cancer Center of Northwestern University. Co-authors on the article include Cancer Center researchers Csaba Gajdos, Alex De Los Reyes, Woochan Park and Alfred W. Rademaker. Rita C. Dardes is affiliated with the Federal University of Sao Paulo, Brazil.

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