As a result, it inhibits the growth of tumour cells and mediates antibody-dependent cellular cytotoxicity in cancer cells exhibiting HER2 protein expression.10,11 Trastuzumab is an approved treatment for breast-cancer and gastric-cancer patients and effective in the subgroup of patients with HER2 overexpression or amplification.12,13. The gene discussed is ERBB2; the disease is breast carcinoma.