Even when a breast cancer patient has only minimal lymph node involvement, additional therapy is needed. If women are not treated with adjuvant systemic therapy like chemotherapy and/or hormonal therapy, disease-free survival is reduced by 10% at 5-year follow-up. These are the main results from the MIRROR study, a Dutch cohort study in which all hospitals from The Netherlands have participated. The results were recently published in the New England Journal of Medicine (de Boer, 2009). The study was supported by a grant from the Netherlands Organization for Health Research and Development (945-06-509).