Biomarkers of neoadjuvant/adjuvant endocrine therapy for ER-positive/HER2-negative breast cancer

Endocrine therapy is one of the key therapeutic components for patients with hormone receptor-positive early stage breast cancer. A lot of efforts have been made in order to explore biomarkers to select optimal endocrine treatment and optimal duration of the treatment. Estrogen receptor (ER) is the most intensively-studied and well-established biomarker for selection of endocrine treatment. Currently, a number of other markers including conventional immunohistochemical markers and molecular markers such as genetic markers and multigene assays have been investigated. Although the clinical utility of PgR expression has been tested in a number of clinical trials of neoadjuvant/adjuvant endocrine therapy, no validated results have been obtained. Oncotype DX Recurrence Score has been reported to be associated with benefit of adjuvant tamoxifen use and the clinical response to neoadjuvant endocrine therapy but more powerful tool is desired for clinical use to optimize endocrine therapy. Neoadjuvant endocrine therapy is considered as a promising strategy to explore biomarkers for endocrine responsiveness as well as to develop a new treatment option in combination with molecular target agents and to study mechanisms underlying endocrine response and resistance. In this manuscript, current understanding on biomarkers of neoadjuvant/adjuvant endocrine therapy for both predictive and prognostic utilities is discussed.