We previously used DNA array analyses in the molecular profiling of breast cancers. By cluster analysis of 55 patients, we identified a subpopulation of breast cancers-designated class A-that contained a high number of nodal-positive tumours and that had frequently developed distant metastases at the time of diagnosis. We have now analysed follow-up data from these patients. We found that, despite a median of only 23.5 months of follow-up, 11 of 22 patients in class A progressed to metastatic disease, and three of five patients classified as having a nodal status of N0 in this subpopulation developed distant metastases. Our analysis identifies breast-cancer patients with a high risk of disease recurrence, and could act as a first step towards improved patient-adapted therapy.