ERBB2 and gastric cancer: Molecular typing of gastric cancer provides an opportunity for individualized treatment of gastric cancer patients, especially markers such as microsatellite instability (MSI), programmed cell death ligand (PD-L1), human epidermal growth factor receptor 2 (HER2), tumor mutation burden (TMB) and mismatch repair deficiency (dMMR) can select gastric cancer patients who would benefit from immunotherapy and targeted therapy.