It has been shown that more than 10% of patients with HER2-negative primary breast cancer may still benefit from HER2-targeted treatment [59], indicating that HER2-negative patients may have metastases that are in fact HER2-positive [60] or that the primary diagnosis is false due to limitations in the IHC staining or in successfully obtaining a representative biopsy. Here, ERBB2 is linked to breast cancer.