OBJECTIVES: I. Compare event-free, recurrence-free, and overall survival following adjuvant therapy with tamoxifen alone vs. tamoxifen plus octreotide long-acting release formulation in postmenopausal women with stage I/II/III breast cancer. II. Compare the toxicity and quality of life associated with each treatment regimen. III. Compare the effects of each treatment regimen on insulin-like growth factor-I (IGF-I) physiology, and study the relationship between IGF-I physiology and outcome.