Trastuzumab monotherapy is used as maintenance therapy for patients with breast cancer based on the study by Vogel et al. [3], who reported an objective response rate of 26 %, which was driven by the response rate in patients with HER2 expression scored as IHC 3+ (35 %); no patient with IHC 2+ expression showed a response. Here, ERBB2 is linked to breast carcinoma.