The initial findings from the Italian trial showed no significant reduction in breast cancer risk with tamoxifen use. However, the National Surgical Adjuvant Breast and Bowel Project’s Breast Cancer Prevention Trial found that tamoxifen reduced the risk of estrogen receptor-positive breast cancer.

Umberto Veronesi, M.D., of the European Institute of Oncology in Milan, and colleagues randomly assigned 5,408 healthy women who had a hysterectomy to receive tamoxifen or a placebo for five years.

After 11 years of follow-up, 136 women developed breast cancer–74 in the placebo group and 62 in the tamoxifen group. Among low-risk women, rates of breast cancer were similar in the tamoxifen and placebo groups. But for women at high risk, breast cancer rates were lower for those taking tamoxifen. Women taking tamoxifen experienced more side effects, including hot flashes and heart problems, than women in the placebo group.

“A complete assessment of the baseline cardiovascular risk should become an important component of counseling women on the use of tamoxifen, particularly in the prevention setting,” the authors write.

Reference: Journal of the National Cancer Institute