Breast cancer hormone receptor levels and benefit from adjuvant tamoxifen in a randomized trial with long-term follow-up

Background: Hormone receptor positivity predicts benefit from endocrine therapy but the knowledge about the long-term survival of patients with different tumor receptor levels is limited. In this study, we describe the 25 years outcome of tamoxifen (TAM) treated patients. Patients and methods: Between 1983 and 1992, a total of 4,610 postmenopausal patients with early-stage breast cancer were randomized to receive totally 2 or 5 years of TAM therapy. After 2 years, 4,124 were alive and free of breast cancer recurrence. Among these, 2,481 had demonstrated estrogen receptor positive (ER+) disease. From 1988, the Abbot enzyme immunoassay became available and provided quantitative receptor levels for 1,210 patients, for which our analyses were done. Results: After 5 years of follow-up, when all TAM treatment was finished, until 15 years of follow-up, breast cancer mortality for patients with ER+ disease was significantly reduced in the 5-year group as compared with the 2-year group (hazard ratios [HR] 0.67, 95% confidence intervals [CI] 0.55–0.83, p