The FDA originally approved trastuzumab to treat BC in September 1998, following a clinical trial in HER2+ metastatic patients in which the addition of trastuzumab to chemotherapy significantly improved the median progression-free survival (PFS) to 7.4 from 4.6 months and the median overall survival (OS) to 25.1 from 20.3 months, as compared with chemotherapy alone [3]. Here, ERBB2 is linked to breast cancer.