Comparative Study for the Degree of Biological Changes After Short-term 2 Weeks and 4 Weeks Preoperative Endocrine Therapy in Luminal Breast Cancer

RATIONALE: Estrogen can promote proliferation of tumor cells in hormone receptors (HR)-positive breast cancer. The standard therapy of Luminal subtypes is endocrine therapy, which can influence proliferation of tumor cells by blocking the use of estrogen by cancer cells or lowering the amount of estrogen the body makes. Thus, markers of proliferation are candidate markers of efficacy after short-term (e.g., 2 weeks or 4 weeks) preoperative hormone therapy. Ki-67 is most commonly used among these markers. In contrast to the absolute value, the degree of Ki-67 changes which consider the baseline values would be better to reflect the sensitivity of therapy. It is not yet known whether the degree of Ki-67 changes after 2 weeks or 4 weeks presurgery endocrine therapy is different and which interval is more suitable to assess therapy sensitivity. PURPOSE: This randomized phase II trial is studying to compare the degree of Ki-67 changes after 2 weeks or 4 weeks preoperative endocrine therapy and to determine a more appropriate interval to assess hormone therapy sensitivity in women who are undergoing surgery for HR-positive, Human epidermal growth factor receptor 2 (HER2)-negative breast cancer.