Trastuzumab is currently licensed in the USA/EU for treatment of patients with HER2-positive early breast cancer (EBC) (in combination with neoadjuvant and/or adjuvant chemotherapy), HER2-positive metastatic breast cancer (MBC) (as monotherapy or in combination with pertuzumab plus docetaxel, or with lapatinib, paclitaxel, docetaxel, or an aromatase inhibitor), and HER2-positive metastatic gastric cancer (in combination with capecitabine or 5-fluorouracil and cisplatin) [3, 4]. Here, ERBB2 is linked to breast carcinoma.