OUTLINE: This is a randomized, double blind, multicenter study. Following 2-3 years of adjuvant treatment with tamoxifen, patients are randomized to receive either oral tamoxifen daily or oral exemestane daily for the remainder of the 5 year period in the absence of disease relapse or unacceptable toxicity. Quality of life is assessed at some centers. Patients are followed at least every 3 months for the first year of treatment, every 6 months for the next two years and then annually thereafter until year 10.