ERBB2 and breast carcinoma: Although T‐DM1 was not superior to taxane in a study of patients with previously treated, HER2‐positive advanced gastric cancer,22 it was an active agent in patients with ERBB2‐mutant/HER2‐overexpressing lung cancers23, 24 and is included as a treatment option for certain patients with non‐breast cancers, such as ERBB2‐mutant metastatic non‐small cell lung cancer and HER2‐positive recurrent or metastatic salivary gland tumors.25, 26