Clinical studies show that increased BAG-1 immunoreactivity is an independent predictor of outcome particularly in node-positive patients with oestrogen receptor (ER) positive breast cancer receiving adjuvant hormonal therapy alone and enhances the predictive power of IHC4 score (a combination of prognostic information derived from ER, PgR, Ki67, and HER2 immunohistochemical staining) [14–16]. This evidence concerns the gene ERBB2 and breast cancer.