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. •Breast cancer is the most common cancer diagnosed in women worldwide.•Risk factors for developing breast cancer include proliferative breast lesions with atypia, hormonal, lifestyle, and genetic factors.•All newly diagnosed breast cancer should be tested for ER, PR and HER2 to define subtype.•Surgical treatment options include breast conservation or mastectomy with axillary management dependent upon nodal status at presentation.•Breast radiation with or without axillary nodal radiation is recommended for most patients who undergo breast conservation.•Endocrine therapy is the mainstay of systemic treatment for patients with hormone receptor positive breast cancer.•HER2 targeted therapy is the mainstay of systemic treatment for patients with HER2-positive breast cancer.•Chemotherapy is the primary systemic treatment for triple negative breast cancer, although immunotherapy may further improve outcomes.