Why most gene expression signatures of tumors have not been useful in the clinic.

Omics technologies are expected to enhance our understanding of a variety of diseases and to open the door to patient-specific personalized medicine. Despite the extensive literature on the use of gene expression arrays to predict prognosis in cancer patients, poor progress has been made in the translation of gene expression signatures for use in the clinics. Breast cancer provides a ripe arena for an analysis of why such signatures have failed to fulfill their promise.