ERBB2 and gastric cancer: In recent years, various biomarker molecules, such as human epidermal growth factor receptor 2 (HER2) and programmed cell death ligand 1 (PD-L1), have been discovered in addition to MSI, and molecular targeted therapies against them have been introduced into clinical practice [14–16]; however, in gastric cancer, the frequency of expression of these biomarkers is often low.