ERBB2 and breast cancer: Based on these findings, as T-Dxd and trastuzumab-duocarmazine demonstrated promising activity in HER2-low breast cancer but no data are currently available on survival endpoints, HER2-low expression in breast cancer can be classified as a tier IIb according to ESMO Scale for Clinical Actionability of molecular Targets (ESCAT), hoping that this evidence could reach a tier I in the future when more solid data on survival endpoints will be available (Mateo et al., 2018; Crimini et al., 2021).