Evidence-based clinical guidelines (S3) and the German Cancer Society certification system for interdisciplinary breast cancer centers have contributed significantly to avoidance of under- or overtreatment of breast cancer. Using the example of current surgical, medical, and radio-oncologic treatment approaches, it is discussed how a risk-adapted reduction of treatment aggressiveness and thus the risk of side effects could be achieved for the patients without compromising the meanwhile very promising therapeutic results. The cycle of scientific evidence, preparation of guidelines, elaboration of quality indicators, and generation of knowledge from clinical practice was successfully concluded for the benefit of the patients.