When routinely applied in all breast cancer patients, it may improve the quality of HER-2 testing by reducing variation in HER-2 testing between labs, serving as a quality control for IHC, identifying gene amplified cases among the IHC 0/1+ patients that will likely respond to trastuzumab as well as IHC 3+ cases without gene amplification that may respond less well to trastuzumab. This evidence concerns the gene ERBB2 and breast cancer.