ERBB2 and breast cancer: Future research urgently requires multinational prospective cohort studies employing standardized testing procedures (e.g., synchronous IHC/FISH testing and NGS validation) and systematically collecting regional environmental exposure, host genetic variation, and molecular typing data to more accurately elucidate the biological heterogeneity and clinical significance of HER2 in biliary tract carcinoma.The efficacy of HER2-targeted drugs in gastric cancer and breast cancer patients with HER2 gene expression has been well-documented.