Results from a study conducted in 155 patients treated with trastuzumab after the development of metastasis or as adjuvant/neoadjuvant treatment showed a correlation between trastuzumab resistance and either deregulation of the PI3K signaling pathway and/or EGFR and IGF-1R overexpression in about 25% of the tumor samples from patients with HER2+ breast cancer [161]. Here, ERBB2 is linked to breast cancer.