HER2 overexpression or amplification in breast cancers is a useful biomarker that has been critical for the identification of patients who are likely to respond to HER2 targeting drugs, thereby enabling the development of trastuzumab [25],[26], pertuzumab [27], trastuzumab-DM1 [28],[29] and lapatinib [30]. Here, ERBB2 is linked to breast cancer.