Using a well-annotated cohort of 177 ERα-positive breast cancer patients who were treated with adjuvant tamoxifen (20 mg/day for 5 years) plus fluoxymesterone (10 mg orally twice per day for 1 year), we found that increased expression of nuclear ERβ1 was associated with prolonged recurrence-free interval. This evidence concerns the gene ESR1 and breast carcinoma.