Patients with resectable, nonmetastatic (stage I-IIIA) breast cancer usually receive adjuvant (postoperative) systemic therapy to control micrometastasis and prevent recurrence. Neoadjuvant (preoperative) chemotherapy is a standard treatment for resectable breast cancer, potentially enabling patients to undergo partial dissection. However, it has been reported that neoadjuvant chemotherapy has a limited effect in patients with hormone receptor-positive disease in terms of pathologic complete response rate, and in elderly patients there may be safety concerns. Furthermore, the appropriateness of chemotherapy for luminal early breast cancer [defined as hormone receptor-positive and human epidermal growth factor receptor-2 (HER2)-negative tumors] is an important clinical issue. We determine the need for chemotherapy in postmenopausal patients with hormone receptor-positive, HER2-negative, lymph node-negative early breast cancer according to clinicopathologic factors, including multigene signature. The National Surgical Adjuvant Study of Breast Cancer (N-SAS-BC06) New primary Endocrine-therapy Origination Study (NEOS) is a randomized phase III trial conducted in Japanese centers. It is evaluating adjuvant endocrine therapy, with or without chemotherapy, in patients with postmenopausal breast cancer that has responded to neoadjuvant letrozole. The aims of this trial are to: define patients who might not require chemotherapy by using their response to neoadjuvant endocrine therapy; analyze the relationship between neoadjuvant endocrine therapy and long-term prognosis; and analyze the correlation between clinical and pathologic response to neoadjuvant hormonal therapy with additional postoperative chemotherapy. We hope that the results of this trial will lead to the development of a new clinical strategy of pre- and postsurgical treatment for luminal breast cancer.