Breast cancer is the most common cancer in women, with an incidence that rises dramatically with age. The average age at diagnosis of breast cancer is 61 years, and the majority of woman who die of breast cancer are age 65 years and older. Major improvements in public health and medical care have resulted in dramatic increases in longevity. The oldest old (those age 80 years and older) are a rapidly expanding group and now comprise 9 million members of the US population. The treatment of individuals who are age 80 years and older is complex and involves clearly defining the goals and value of treatment while also weighing risks, such as the potential effects of treatment on functional loss and quality of life. Limited evidence-based treatment guidelines exist for the caring of this older cohort of patients with breast cancer. Data from clinical trials that enroll primarily younger patients lack the information needed to estimate the likelihood of toxicities that can be life changing in older adults. Clinicians who make treatment recommendations should place the available evidence in the context of the patient's life expectancy and geriatric assessment results that include an evaluation of a patient's functional status, comorbidities, cognition, social support, nutritional status, and psychological state. Furthermore, these decisions should be placed in the context of the patient's goals for treatment, preferences, and values. This review summarizes the current literature and focuses on the role of geriatric assessment in treatment recommendations for patients age 80 years and older with early and metastatic breast cancer.