The use of gene-expression microarray analysis to assess the expression levels of all the genes in the genome has tremendous potential. Important information has been obtained about many disease processes, particularly in classifying tumors in different subtypes and risk groups. Combining gene-expression data with other genomic information and the use of sophisticated bioinformatic tools enables the discovery of potential new targets for treatment, and is helpful for high-throughput drug screening and for designing new classes of drugs for targeted therapy. Here, we provide a short overview of the recent, promising developments in the field with emphasis on breast cancer.