However, many patients are unable to experience the benefits of trastuzumab treatment, because the HER2-overexpression rate [immunohistochemistry (IHC) score: 2+; fluorescent in situ hybridization-positive or IHC score: 3+] in gastric cancer patients ranges only from 12.1% to 15.6% [9, 10]. The gene discussed is ERBB2; the disease is gastric cancer.