Abstract
This report reviewed early findings in five randomized trials comparing tamoxifen or raloxifene with placebo for preventing breast cancer. In addition, information on side effects and new cancers in the other breast is available from 11 adjuvant trials that evaluated tamoxifen therapy for 3 years or longer. The prevention trials administered 20 mg tamoxifen per day for at least 5 years. Daily doses in the adjuvant trials ranged from 20 to 40 mg. Analysis of the findings pointed to a 30% to 40% reduction in the incidence of breast cancer in the four prevention trials evaluating tamoxifen. The figure was 38% when data were analyzed using a fixed-effect model and 34% when using a random-effects model. The adjuvant studies demonstrated a 46% lower incidence with tamoxifen. Raloxifene therapy led to an even greater reduction in breast cancer incidence of 64%. Estrogen receptor (ER)-positive cancers were reduced by 48% in the tamoxifen prevention trials, whereas there was no reduction in ER-negative cancers. Age was not a significant factor. Endometrial cancers were increased in all tamoxifen prevention trials, with a relative risk of 2.4. No such effect was apparent with raloxifene. In adjuvant studies the hazard ratio was 3.4. The excess risk was concentrated in women aged 50 and older. Venous thromboembolism was more frequent in all studies. The RR in tamoxifen prevention trials was 1.9. Substantial variation in mortality rates was noted. There was no overall effect on all-cause modality in the tamoxifen prevention trials, but heterogeneity was high. Deaths from endometrial or other cancers or cardiovascular events were not excessive with the exception of pulmonary embolism. At present tamoxifen cannot be recommended for preventive use, except possibly for women at very high risk who prefer to avoid, or at least delay, prophylactic mastectomy. Adjuvant tamoxifen therapy for women with breast cancer continues to have a favorable cost-benefit profile.
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