It may be difficult to achieve complete cure for most metastatic breast cancer patients;thus, prolongation of overall survival and maintenance of the quality of life are often the main focus of treatment. In the treatment of metastatic breast cancer patients, it is important to choose the most appropriate therapeutic strategy based on substantial evidence that considers the biology of the tumor, including estrogen receptor(ER), progesterone receptor(PgR), and human epidermal growth factor receptor 2(HER2)status;the site and extent of the metastatic focus;the time to recurrence;prior treatment regimens;age; menopausal status;performance status;and the preference of the patient. A clinical subtype classification that is based on the tumor biology is typically utilized for devising a treatment strategy specific to each subtype. Expressly, first-line treatment options may include hormone therapy for hormone-positive breast cancers, antiHER2 therapy for HER2-positive breast cancers, and chemotherapy for hormone-negative and HER2-negative(triple negative)breast cancers. In recent years, with the development of regimens that are effective for every subtype, the treatments for breast cancer have undergone significant changes. In this section, we introduce the progress in the treatment for metastatic breast cancer, focusing specifically on second-line therapies according to each subtype.