The control of breast cancer: the role of tamoxifen.

The worldwide burden of breast cancer, already substantial, is increasing in both developed and developing countries. By the year 2000, there will be close to one million new diagnoses and over 400,000 deaths per year. Control measures must be directed toward primary prevention, early diagnosis, and effective therapy. Tamoxifen is an effective treatment for early and advanced disease, it has few side effects, it has a low cost, and it is easy to administer. In early breast cancer tamoxifen produces a 25% reduction in relapse rates and a 17% reduction in mortality rates. This benefit is greater for women with estrogen receptor-positive tumors and with therapy duration longer than 2 years. It is also effective in premenopausal and postmenopausal women, including those over 70 years of age. It reduces the risk of new contralateral cancers, and it is being evaluated as a preventative agent in women at high risk for breast cancer. Tamoxifen has a particularly valuable role in developing countries in which the incidence of breast cancer is increasing as the average age of the population increases and in which control is substantially more difficult with mass mammography screening.