SEATTLE-A group of breast cancer patients treated with tamoxifen(Drug information on tamoxifen) (Nolvadex) outside of clinical trials had up to a 60% reduction in their risk of developing cancer in the contralateral breast and no increased risk of ovarian or endometrial cancer, report Linda S. Cook, PhD, and her colleagues at the Fred Hutchinson Cancer Research Center.
The study provides reassurance about the safety of short-term tamoxifen therapy in conventional medical practice, but since the average duration of tamoxifen treatment was less than 2 years in this group, the results shed no light on possible adverse effects from long-term use.
The Seattle researchers used cancer registry and medical record data to identify a cohort of 12,598 women in western Washington state under age 85 who were diagnosed with primary breast cancer between 1978 and 1990. Of these, 39 women developed ovarian cancer, 42 endometrial cancer, and 234 contralateral breast cancer prior to 1992.
The case subjects who had developed the second primary cancers were matched by age, disease stage, and year of initial breast cancer diagnosis with control subjects drawn from the same cohort.
The percentage of women who had received tamoxifen was 10% and 18%, respectively, among contralateral breast cancer subjects and controls; 18% and 20%, respectively, among ovarian cancer subjects and controls; and 26% and 31%, respectively, among endometrial cancer subjects and controls (J Natl Cancer Inst 87:1359-1364, 1995).
The overall reduction in risk for contralateral breast cancer with any use of tamoxifen was 50%, with reductions of 60% seen for women who used the agent for more than 1 year and for those who continued therapy through the end of study follow-up or stopped therapy less than 1 year before the end of follow-up.
Risk reductions were larger in post-menopausal than in premenopausal women, although the data suggest that tamoxifen use of more than 1 year's duration reduces the risk in premenopausal women as well.