ERBB2 and breast cancer: HER2 is amplified or overexpressed in 20–30% of all breast cancer patients and is sensitive to HER2 inhibitors, such as trastuzumab, pertuzumab, trastuzumab emtansine, and fam-trastuzumab deruxtecan (Alpuim Costa et al, 2021; Dumbrava et al, 2019).