Women whose breast cancer is treated with tamoxifen face a heightened risk for endometrial cancer, with that risk compounded in women who also have received estrogen replacement therapy or who are obese, according to a study led by University of Southern California researchers.
Leslie Bernstein, Ph.D., professor of preventive medicine at the Keck School of Medicine of the University of Southern California and USC/Norris Comprehensive Cancer Center, and colleagues present these findings in the Oct. 6 issue of the Journal of the National Cancer Institute.
Doctors prescribe tamoxifen, a synthetic hormone, to women as a breast cancer treatment because of its proven benefits for blocking a recurrence of the disease, reducing the likelihood of a second breast cancer developing in the opposite breast and extending patients' survival. It is also under study as a preventive agent against breast cancer in women at high risk for the disease. However, this study indicates the same drug increases the risk of endometrial cancer, the most frequent gynecologic cancer in women.
"Because tamoxifen is a critical therapeutic option for breast cancer patients, we need to understand its other effects on the body," Bernstein said. "Although we have known that endometrial or uterine cancer develops in a tiny proportion of women taking tamoxifen, we have not known which particular groups of women are at greatest risk of this disease."
Overall, the authors report that tamoxifen therapy for breast cancer increased the risk of endometrial cancer by about 50 percent. The longer women are on tamoxifen therapy, the greater their risk: women with more than five years of exposure to tamoxifen were four times more likely to develop endometrial cancer than women who did not use tamoxifen. But a woman's risk of endometrial cancer also varies according to other characteristics.