Inclusion Criteria:  Histopathologically and immunohistochemically confirmed ER+ and HER2- Premenopausal BC patients Tumor size >0.5cm on USG Stage I-IIIA BC and planned curative surgery ECOG 0-2  Patients with adequate bone marrow function  - Hemoglobin 10 g/dL, ANC 1,500/mm3, Plt 100,000/mm3  Patients with adequate kidney function  - serum Cr ≤ 1.5 mg/dL  Patients with adequate liver function  Bilirubin: ≤ 1.5 times of upper normal limit AST/ALT: ≤ 1.5 times of upper normal limit Alkaline phosphatase: ≤ 1.5 times of upper normal limit Patients who decided to voluntarily participate in this trial with written informed consent Premenopausal women : women who has not removed both ovaries, women who had menses in recent 1 year and FSH level is less than 30mIU/ml  Exclusion Criteria:  Previous history of ipsilateral invasive breast cancer, in situ lesion Previous history of chemotherapy or endocrine therapy on contralateral BC for the past 2 years Patients who has distant metastasis Patients who is pregnant or breastfeeding Hormon receptor negative BC Her-2 positive BC Diagnosed pituitary adenoma Women who has endometriosis, uterine myoma, unknown vaginal bleeding Inability to understand and willingness to sign a written informed consent Patients with endometriosis, uterine fibroids, or unexplained vaginal bleeding Patients with a history of bleeding constitution, coagulopathy, or thromboembolism Patients who have administered a CYP3A inhibitor or inducer, CYP2D6 inhibitor, etc. within 4 weeks prior to randomization