ABSTRACT
Over the past three decades, the antiestrogen tamoxifen, which belongs to the first generation of selective ER modulators (SERMs) and which acts as an estrogen antagonist on the breast, has been the gold standard for the endocrine treatment of all stages of these cancers. Tamoxifen acts as a SERM by blocking the AF-2 domain of ER but does not inhibit AF-1 activity (Figure 9.1). The benefits of tamoxifen and chemotherapy in women who have node-negative ERα-positive breast cancer have been demonstrated in large clinical trials such as the National Surgical Adjuvant Breast and Bowel Project (NSABP) trials B-14 and B-20.2,3 Five years of tamoxifen started
immediately after surgery for early stage ER-positive breast cancer was shown to reduce recurrence by 51% and mortality by 28%.4
