A cost effectiveness study [14] demonstrated Trastuzumab deruxtecan to be a cost-effective alternative to trastuzumab emtansine as a second-line treatment for cases with human epidermal growth factor receptor 2 (conventionally labelled HER2) overexpression, i.e., 20% of breast cancer cases with worse overall survival outcomes. The gene discussed is ERBB2; the disease is breast carcinoma.