During the last 2 decades, the outcome of patients with early-stage ERBB2/HER2-positive breast cancer has markedly improved owing to new treatment strategies combining polychemotherapy and multiple ERBB2/HER2-targeted drugs.1,2,3,4,5,6,7,8,9,10 However, it is increasingly evident that many patients are overtreated by the recommended regimens, whereas others still experience metastatic relapse. This evidence concerns the gene ERBB2 and breast cancer.