While the majority of breast cancer patients with histologically lymph node-negative cancers are cured by local therapy alone, approximately 25% will develop recurrent breast cancer and die of their disease in the absence of systemic adjuvant chemotherapy [1]. Cytotoxic chemotherapy markedly improves outcome for some of these patients. Assays that could better distinguish those nodenegative patients who are more likely to suffer distant recurrence could prove very useful in optimizing patient selection for chemotherapy. Technologies based on DNA microarray analysis using polymerase chain reaction (PCR) amplification seem like ideal candidates for the development of novel prognostic and predictive assays. The Oncotype DX TM test is a clinically validated, multigene assay performed on samples processed from primary invasive breast carcinomas. The assay provides a quantitative assessment of the likelihood of distant breast cancer recurrence in women with estrogen receptor-positive, node-negative disease, and also assesses the potential benefit from chemotherapy in these women [2]. A major strength of its 21-gene recurrence score is that it has been tested against outcomes data derived from the NSABP-B20 randomized trial in which cancer recurrence and survival is already known with several years of clinical follow-up. It seems likely that future assays will be developed using similar technology to address important clinical questions related to staging and cancer therapy.