ERBB2 and breast carcinoma: For example, trastuzumab‐deruxtecan (T‐DXd) has shown efficacy in patients with HER2‐low breast cancer, defined as HER2 immunohistochemistry (IHC) 1+ or 2+/situ hybridization (ISH) negative, which was recognized as HER2‐negative in the past.5