Neo-adjuvant Chemotherapy With Letrozole in Patients With Estrogen Receptor Positive/HER-2 Negative Breast Cancer

Inclusion Criteria: * Pathologically proven breast cancer patients who are candidate of neoadjuvant chemotherapy with AC followed by Docetaxel * Age: 19-70 years * ER or PR positive ,cT2-3N0 or cT1-3/N+ M0 (ER-positive ≥1% nuclear staining by immunohistochemistry , Allred score≥3 ) * Available FFPE tissue for biomarker study * HER2-negative by ASCO/CAP guideline * Patients who agree to adequate contraception * ECOG scores of 0-2 * Normal or acceptable kidney, liver, cardiovascular, and bone marrow functions * Patients who provide consent Exclusion Criteria: * Inflammatory breast cancer * Distant metastasis * Cerebral vascular accidents including transient ischemic attack * Pulmanary thromboembolism or deep vein thrombosis with 6 months; however, patients who received more than 6 weeks of anticoagulation within 6 months and remains asymptomatic are eligible. * With a history of malignant tumor or complicated with other malignant tumors in addition to breast cancer, except for non-melanoma skin cancer, curatively resected early gastric cancer, differentiated thyoid cancer \< 1 cm, or other cured malignant tumor without recurrence for at least 3 years * Ejection Fraction \<55% by MUGA scan / Echo CG * No available tissue for biomarker study * Pregnant or lactating women * Patients with other serious diseases or medical conditions: Pituitary adenoma, Malabsorption syndrome, Major resection of gastrointestinal tract, Corrected QT interval \> 480 msec, Congestive heart failure or unstable angina pectoris, myocardial infarction, stent insertion, angioplasty, coronary bypass surgery, symptomatic peripheral artery disease within 6 months before the enrollment * NYHA class III or IV congestive heart failure * Uncontrolled hypertension and uncontrolled high-risk arrhythmia considered by the investigator * Major surgery, major trauma, and/or unhealed wound, fracture, or ulcer within 4 weeks * Acute hemorrhage or hemorrhagic tendency * Obvious neurological or psychiatric disorders, including psychosis, epileptic dementia and other diseases which may affect the understanding and sign of the informed consent * Uncontrolled acute infection * Patients with allergic constitution and any known or suspected drug allergy * Concurrent use of other investigational drugs; or participating in other clinical trials involving investigational drugs within 30 days before this study * Patients with mental illness or other conditions affecting the patient compliance * Not suitable for the trial considered by the investigator