Breast cancer management in 2021: A primer for the obstetrics and gynecology.

Breast cancer is the most commonly diagnosed cancer and is the leading cause of cancer death in women worldwide. Several factors increase the risk of breast cancer development, including patient characteristics, lifestyle habits, and predisposing genetic mutations. Once a diagnosis of breast cancer has been established, treatment decisions are guided by breast cancer stage and phenotype. Immunohistochemistry is used to quantify estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor 2 (HER2) expressions. In this chapter, we will focus on the management of localized and metastatic breast cancer, guided by the breast cancer hormone receptor status (ER and PR expression) and HER2 expression identified at diagnosis.