The target population included all those receiving a second or later line of treatment for advanced gastric cancer, regardless of the specific biomarkers that can guide the effective treatment [70], (i.e., HER-2 overexpression, high levels of microsatellite instability (MSI-H), mismatch repair deficiency (dMMR), programmed death ligand 1 (PD-L1) overexpression, and fibroblast growth factor receptor (FGFR) alterations). This evidence concerns the gene ERBB2 and gastric cancer.