Recurrences May Be More Difficult To Treat In Women Who Take Tamoxifen, Study Suggests.(breast cancer relapses)

2001 AUG 9 - (NewsRx Network) -- A new study from the Fred Hutchinson Cancer Research Center confirms that tamoxifen use decreases the risk of a second breast cancer, but it also finds that the drug may cause a fivefold increased risk of estrogen-receptor (ER)-negative breast cancer a cancer that is more difficult to treat - in the breast opposite, or contralateral, to the initial tumor.

The study follows research in recent years indicating tamoxifen improves survival and reduces risk of recurrence among women diagnosed with breast cancer.

Christopher Li, MD, and colleagues in the Hutchinson Center's Public Health Sciences Division, Seattle, Washington, reported their findings in the July 4, 2001, issue of the Journal of the National Cancer Institute. This population-based study was funded by a grant from The Life Possibilities Fund.

Comparing breast-cancer patients who received tamoxifen to those who did not, Li and colleagues found that while the drug appeared to cause a 20% reduction in ER-positive contralateral breast cancer - the more common type - it also appeared to increase the risk of ER-negative contralateral tumors by nearly 500%.

"Among women who take tamoxifen after an initial breast-cancer diagnosis, our study and numerous random trials suggest that tamoxifen will decrease a woman's risk of developing cancer in the other breast," Li said. "But if they do develop a tumor on the opposite side, our study suggests that the cancer is more likely to be ER-negative, which is associated with a higher mortality risk."

The researchers' data analysis showed that 27% of the contralateral tumors that developed in tamoxifen users were ER-negative, while only 4% of the contralateral tumors that developed in non-users were ER-negative. Li, a postdoctoral fellow in epidemiology at the Hutchinson Center and at the University of Washington School of Public Health and Community Medicine, cautioned that the study shouldn't alter what physicians recommend to their patients.

"While this study, if confirmed by others, adds to our knowledge about the effects of tamoxifen, I do not believe it should change current clinical practices, as tamoxifen has clearly been shown to reduce the risk of recurrence and improve survival among women diagnosed with breast cancer," he said.