Breast cancer is the leading cause of death from cancer in women worldwide, and the second most common cause of death from cancer in women in the United States. Risk assessment tools can identify the risk of breast cancer, and patients at high risk may be candidates for risk-reducing medications. The choice of medication varies with menopausal status. Breast cancer treatment depends on the stage. Stage 0 is ductal carcinoma in situ, which is noninvasive but progresses to invasive cancer in up to 40% of patients. Ductal carcinoma in situ is treated with lumpectomy and radiation or with mastectomy. If ductal carcinoma in situ is estrogen receptor-positive, patients may also receive endocrine therapy. Early invasive stages (I, IIa, IIb) and locally advanced stages (IIIa, IIIb, IIIc) are nonmetastatic and have three treatment phases. The preoperative phase uses systemic endocrine or immunotherapies when tumors express estrogen, progesterone, or ERBB2 receptors. Preoperative chemotherapy may also be used and is the only option when tumors have none of those three receptors. There are two options for the surgical phase with similar survival rates; a lumpectomy with radiation if the tumor can be excised completely with good cosmetic results, or a mastectomy. Sentinel lymph node biopsy is also performed when there is suspected nodal disease. The postoperative phase includes radiation, endocrine therapy, immunotherapy, and chemotherapy. Postmenopausal women should also be offered postoperative bisphosphonates. Stage IV (metastatic) breast cancer is treatable but not curable. Treatment goals include improving the length and quality of life.