Résumé : The microarray technology has enabled scientists to simultaneously investigate the expression of thousands of genes. Regarding breast cancer, this technology has provided a molecular classification into clinically relevant subtypes, new tools to predict disease outcome and response to treatment and new insights into carcinogenesis and metastatic progression pathways. Here we describe the state of the art of gene expression profiling for breast cancer, and we discuss the potential impact on breast cancer patient management considering its limits and promises.