Breast cancer remains the leading cause of new cancer cases in women and is responsible for the most cancer-related deaths in women worldwide. The goals of breast cancer treatment are to maintain or improve quality of life, prolong survival, and increase disease-free progression. The majority of breast cancer cases are estrogen receptor (ER)-positive and human epidermal growth factor receptor-2 (HER-2)-negative, and current treatment guidelines recommend multiple lines of endocrine therapy followed by chemotherapy in patients with locally recurrent or metastatic disease