Pertuzumab is used in combination with eithertrastuzumab or ado-trastuzumab emtansine for the neoadjuvant treatmentof metastatic HER2-positive breast cancer.1−4 Having a similar mechanism ofaction as trastuzumab, pertuzumab selectively binds subdomain II ofthe HER2 extracellular domain (ECD). Here, ERBB2 is linked to breast cancer.