Metastatic breast cancer (MBC) is incurable. Although first-line endocrine therapy is preferred to hormone receptor positive (HR+), human epidermal growth factor receptor-2 negative (HER2-) MBC, combination chemotherapy should be reserved as the initial treatment for patients with rapid clinical progression, life-threatening visceral metastases, and need for rapidly symptom control. Either prolonged chemotherapy or endocrine therapy may be used as maintenance after disease control. However, which maintenance strategy is superior in terms of delaying disease progression as well as maintaining quality of life (QOL) remains uncertain. This phase III trial aims to compare the efficacy and safety of fulvestrant or capecitabine as maintenance therapy after first-line combined chemotherapy in HR+/HER2- MBC.