Strategies and Progress of Endocrine Therapy for Patients with Metastatic Breast Cancer

Breast cancer is one of the most prevalent cancers and the leading causes of cancer mortality in women worldwide and in China. For hormone receptor-positive (HR+) breast cancer, accounting for approximately 60-80% of breast cancer, endocrine therapy (ET) is the primary treatment strategy. For patients with HR+ metastatic breast cancer (MBC), there are many endocrine-based treatment options that can improve long-term outcomes and optimize quality of life. With the emergence and availability of new and effective agents, the options for ET have expanded in the last two decades. Although hormone therapy has been a standard of care for many decades, treatment must be individualized based on tumor biology and extent of disease. For example, the patients with impending organ failure may be treated with induction chemotherapy to improve organ function, followed by ET. For the patients who develop metastatic disease while on adjuvant ET, particularly when associated with organ failure, or for those with low expression of hormone receptors or expression of HER2, chemotherapy again may be a preferred initial treatment. ET blocks estrogen-driven tumor growth through different mechanisms; however, HR+ MBC can be intrinsically resistant or may acquire resistance to the treatment. Several targeted agents have been approved to use in combination with ET to improve response and delay development of resistance.