 This multicenter, randomized, comparative study will evaluate the efficacy of denosumab to prevent the adjuvant therapy of aromatase inhibitors-induced loss of bone mineral density BMD in breast cancer patients with normal BMD. Investigators will compare the inhibitory effects of denosumab on bone loss between participants with normal BMD to whom Letrozole or Arimidex will be administered as postoperative endocrine therapy for stage I-IIIA postmenopausal hormone-sensitive breast cancer and controls. 