ABSTRACT
Neo-adjuvant endocrine therapy was historically used to treat oestrogen receptor-positive tumours in patients considered inoperable or unfit for surgery. Today, one of the main clinical indications is to downstage tumours in women who might otherwise require a mastectomy and facilitate breast conservation surgery. Pre-menopausal patients with larger cancers generally have an indication for chemotherapy and experience is therefore greatest in post-menopausal women. Responses are greater in tumours with high levels of oestrogen receptor expression and depend on the anti-proliferative effects of oestrogen withdrawal. Treatment within the pre-operative period has also allowed a unique opportunity to characterise biomarkers of response to endocrine therapy. On-treatment changes in Ki67 (a marker of proliferation) have been correlated with long-term outcomes and incorporated into the Pre-operative Endocrine Prognostic Index. These biomarkers have been used in the design of novel neo-adjuvant endocrine studies as a method of interrogating mechanisms of endocrine resistance and accelerating drug development for high-risk disease.
