Scientists and clinicians are familiar with Affymetrix Genechip™ arrays being utilized predominantly in the areas of basic research, target discovery, and target validation. Recently, however, studies are being conducted and published using this research use only platform in clinical research, including phase II and phase III clinical trials. During this presentation, two breast cancer studies will be reviewed. One study utilizes gene expression profiling for predicting therapeutic response to docetaxel [1]. The other study, loss of heterozygosity in breast cancer, utilizes our new DNA analysis array for mapping over 10,000 single nucleotide polymorphisms in the human genome.