ERBB2 and breast carcinoma: More recently, beyond the striking and established efficacy of HER2-directed therapies in HER2+ breast cancer, the possibility of targeting HER2 has been explored also in HER2-low breast cancer (Fusco et al., 2013; Fusco and Bosari 2016; Meric-Bernstam et al., 2019; Kreutzfeldt et al., 2020; Sartore-Bianchi et al., 2020; Shitara et al., 2020; Siena et al., 2021).