A cohort of 177 postmenopausal women with early stage ERα-positive breast cancer enrolled onto NCCTG 89-30-52 who were randomized to the adjuvant treatment with tamoxifen plus fluoxymesterone arm (C3) was used to assess whether ERβ1 expression is associated with the likelihood of a breast cancer event (local, regional or distant recurrence). Here, ESR1 is linked to breast carcinoma.