As the US population ages over the next quarter century, the number of older adults with breast cancer is expected to grow. The challenge in providing care for older adults with breast and other cancers is that there is less evidence-based data about the risks and benefits of therapy, since older adults have been under-represented in clinical trials. However, several recent studies have contributed to our knowledge about the optimal care for these patients. This article will highlight the studies that are beginning to shed some light on the specific risks and benefits of adjuvant breast cancer therapy in older adults and review the physiologic changes with aging that can affect tolerance to cancer therapy.