ABSTRACT
Women (n = 13 388) at increased risk of breast cancer according to Gail’s algorithm were randomly assigned to receive placebo or tamoxifen 20 mg/day for 5 years to assess the possible role of tamoxifen in breast cancer prevention. After a mean follow-up time of 47.7 months, tamoxifen reduced the risk of invasive breast cancer by 49% (p 0.000 01). Risk was reduced in women aged less than 50 years (44%), 50-59 years (51%) and 60 years or older (55%). The risk of non-invasive breast cancer was also reduced by 50%. The effect of tamoxifen on invasive breast cancer was confined to ER-positive tumours (69% reduction). There was no reduction in the rate of ischaemic heart disease, but a reduction in hip, radius and spine fractures was observed. Endometrial cancer incidence was higher (RR, 2.53; CI, 1.35-4.97), predominantly in women older than 50 years. Rates of stroke, pulmonary embolism and deep vein thrombosis were also increased with tamoxifen. The results unequivocally demonstrate that tamoxifen decreased the early incidence of invasive and noninvasive breast cancer in this population.
