DNA microarray technology is revolutionizing the way fundamental biologic questions are addressed in the postgenomic era. In this study by Hedenfalk et al., the authors attempted to identify discrete gene expression profiles for patients with known hereditary breast cancers caused by mutations inBRCA1andBRCA2, both of which increase the lifetime risk of developing breast cancer. The genome-wide perspective identified discrete sets of genes that discriminated betweenBRCA, BRCA2,and sporadic breast tumors. This commentary discusses some limitations of studying a small number of cases. The authors also address the need for validation on independent tumor sets, and the potential benefit of multivariable-type analyses to consider other potential confounding factors such as tumor grade, receptor status, tumor stage, and treatment information.