Neoadjuvant Endocrine Therapy in Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2 (HER2)-Negative Node-Negative Breast Cancer

STUDY RATIONALE: Patients with hormone receptor (HR)+, HER2- node-negative breast cancers generally undergo surgical resection upfront, followed by adjuvant chemotherapy, if needed, in addition to adjuvant endocrine therapy. Because endocrine therapy is primarily delivered in the postoperative setting, the ability to assess the tumor response to this treatment modality is lost and very difficult to assess. This study offers the unique opportunity to assess the responsiveness of breast tumors to endocrine therapy while the tumors are still in vivo by treating patients with endocrine therapy before surgery and assessing molecular changes with treatment. By comparing pre- and post-treatment levels of molecular markers in individual tumors, the team expects to identify predictors of responsiveness to existing agents and identify new candidate therapeutic targets. PRIMARY OBJECTIVE: The primary objective is to determine the frequency of increased HER family of receptor tyrosine kinases protein expression in tumors, following treatment with neoadjuvant endocrine therapy and their correlation with Ki-67 tumor responses. The team will measure cancer cell protein levels of growth factor receptors of the human epidermal growth factor receptor (HER) family before and after neoadjuvant endocrine therapy. The data will be used to inform a future randomized trial of combined endocrine and the most promising anti-HER targeted therapy.