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

BackgroundAdjuvant 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 methodsPremenopausal 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.ResultsIn 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 <40 years of age (HR 0.09, p = 0.02). A risk reduction was also seen in women 40–49 years of age or ?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.ConclusionIn 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 <40 years of age. The effect of tamoxifen was not significantly dependent on time.