The therapeutic options for patients with noninvasive or invasive breast cancer are complex and varied. In many situations, the patient and physician are responsible for jointly exploring and selecting the most appropriate option from among the available alternatives. With rare exceptions, the evaluation, treatment, and follow-up recommendations in these guidelines are based on the results of past and present clinical trials. However, not a single clinical situation exists in which the treatment of breast cancer has been optimized with respect to either maximizing cure or minimizing toxicity and disfigurement. Therefore, patient and physician participation in prospective clinical trials allows patients to not only receive state-of-the-art cancer treatment but also contribute to improving the treatment of future patients. © Journal of the National Comprehensive Cancer Network.