[A randomized clinical trial of adjuvant endocrine therapy after breast conserving surgery for early breast cancer. Cooperative Study Group for Breast Conserving Therapy].

To evaluate the clinical efficacy of adjuvant endocrine therapy after breast conserving surgery for early breast cancer, we have conducted a randomized controlled study since 1989. One hundred twelve-patients having a small breast tumor, less than 2 cm in diameter, and no palpable axillary lymph node, were the subjects of this study. All these patients underwent partial mastectomy with axillary lymph node dissection and were randomly divided into two groups according to the type of postoperative adjuvant endocrine therapy: Group I, tamoxifen (20 mg/day) for 2 years; Group II, no tamoxifen administration. The median follow-up period was 32.2 months. The incidence of local recurrence in the ipsilateral breast was 1.9% in Group I, which was lower than in Group II (6.8%). Three-year disease-free survival rates were also more favorable in Group I (94.2%) than in Group II (88.9%). This difference in prognosis was evident in patients with ER-positive tumors but not related to the menopausal status. These results suggest that adjuvant endocrine therapy with tamoxifen may be recommended for patients who underwent breast conserving surgery for early breast cancer, especially in those with ER-positive tumors.