A Study to Evaluate Exemestane Tablets Combined With Ovarian Function Suppression/Ablation in Treatment of Premenopausal Breast Cancer Patients With CYP2D6*10 Mutations （STEP）

Inclusion Criteria: * Providing informed consent forms voluntarily before screening evaluation; * For Chinese premenopausal women, her estradiol level must be within the premenopausal level, or the patient meet the following 4 criteria in the prior 6 months: No chemotherapy, Regular menstruation, No use of hormonal, contraceptives, No use of hormone for treatment or for temporary amenorrhea caused by chemotherapy, the estradiol level tested within 8 months after the last dose of chemotherapeutics is within the premenopausal level; * Patients with invasive breast cancer which has been confirmed by histological examination; * Complete removal of tumor by surgery without local residual; * Neoadjuvant chemotherapy before surgery is permitted if the surgery for primary breast cancer is performed within 12 weeks without any further adjuvant chemotherapy, or adjuvant chemotherapy is completed within 8 months; * Estrogen receptor (ER) and/or progesterone receptor (PR) positive: If the patient has more than one breast tumor lesions, each tumor lesion should be ER and/or PR positive. * Her-2 negative; * Genotyping test performed by the central laboratory designated by sponsor with the results confirmed as CYP2D6\*10T/T gene mutation. * Women of childbearing age with negative serum pregnancy test result, and agreeing to adopt highly efficient non-hormonal contraception measure throughout the study; * Subject without major organ dysfunction, and with normal heart, liver, kidney, lung an…