In this study, the combined detection of gastroscopy, MSCT, immunohistochemical marker HER-2, and tumor markers of carbohydrate antigen 199 (CA199), CA242, CA724, and carcino-embryonic antigen (CEA) was performed to observe and analyze the clinical effect of the diagnosis of gastric cancer staging, providing a basis for clinicians to select a reasonable treatment plan, with the report below. The gene discussed is ERBB2; the disease is gastric cancer.