A new study done in mice suggests that taking raloxifene after 5 years of tamoxifen therapy may not further prevent the growth of breast cancers. What's more, raloxifene may stimulate the growth of endometrial tumors, conclude Ruth M. O'Regan, M.D., and V. Craig Jordan, Ph.D., D.Sc., of Northwestern University Medical School, Chicago, and their colleagues in the Feb. 20 issue of the Journal of the National Cancer Institute.

Adjuvant therapy with the selective estrogen receptor modulator tamoxifen helps some women with early-stage breast cancer reduce their risk of recurrence. But some studies have suggested this benefit levels off after 5 years, and further treatment with tamoxifen not only doesn't help, it may increase a woman's risk of endometrial cancer.

To get around this, researchers have suggested following a 5-year tamoxifen treatment with the SERM raloxifene, a drug used to prevent osteoporosis in postmenopausal women. Results from a large randomized clinical trial of raloxifene suggested that the drug may decrease a woman's risk of breast cancer without increasing her risk of endometrial cancer.

However, the new study suggests that raloxifene after tamoxifen may not be beneficial. O'Regan and her colleagues exposed breast and endometrial tumors in mice to combinations of estrogen, tamoxifen, and raloxifene or nothing at all. The authors found that raloxifene did not further prevent the growth of breast tumors previously exposed to more than 5 years of tamoxifen. Furthermore, raloxifene did not block the growth of endometrial tumors caused by low-dose estrogen. The authors conclude that treatment with raloxifene after 5 years of tamoxifen treatments may not further decrease breast cancer recurrence and may increase the incidence of endometrial cancer.

These findings "do not support an optimistic future for the use of raloxifene as a replacement for tamoxifen after 5 years of adjuvant therapy," says Michael B. Sporn, M
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Contact: Linda Wang
jncinews@oup-usa.org
301-594-2927
Journal of the National Cancer Institute
19-Feb-2002

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