Overexpression of HER2 leads to abnormal cell growth and proliferation, which may be associated with the development of carcinogenesis, and HER2 overexpression is frequently seen in breast and gastric cancers, but less common in NSCLC patients, with an incidence of less than 5% (Takegawa and Yonesaka, 2017). The gene discussed is ERBB2; the disease is gastric cancer.