Tamoxifen reduces the risk of contralateral breast cancer in premenopausal women: Results from a controlled randomised trial.

BACKGROUND: Adjuvant treatment with tamoxifen reduces the risk of contralateral breast cancer in hormone-responsive postmenopausal patients, whereas the effect in premenopausal women has not been fully elucidated. We have therefore studied the effect of tamoxifen on contralateral breast cancer in premenopausal women in a controlled randomised trial. PATIENTS AND METHODS: Premenopausal women (564) with stage II breast cancers were randomised to 2 years of tamoxifen versus control irrespective of oestrogen receptor (ER) and progesterone receptor (PgR) status. The median follow-up for patients not developing a contralateral cancer was 14 years. RESULTS: In the control group 35 women, and in the tamoxifen group 17 women, developed a contralateral breast cancer as a primary event. Tamoxifen significantly reduced the risk of contralateral breast cancer in all women regardless of age (hazard ratio (HR) 0.5, p=0.02). In subgroup analysis the risk reduction was most pronounced in patients /=50 years of age, although in these subgroups this did not reach statistical significance. The reduced risk of contralateral breast cancer was persistent during the whole follow-up time. CONCLUSION: In this randomised trial, adjuvant treatment using tamoxifen for 2 years reduced the incidence of contralateral breast cancer by 50% in all premenopausal women, and by 90% in women