Despite the development of new treatment options, a significant number of patients lack these targetable biomarkers: the frequency of HER2 expression in gastric cancer is heterogeneous, ranging from 4.4% to 53.4%, with the mean being 17.9% [9]; only 10 to 22% of gastric tumors present MSI [10]; and although PD-L1 positivity in gastric cancer at a cutoff of CPS ≥ 1 has been frequently observed in clinical trials, ranging from 60.4% to 85.1% [11], the clinical benefits of immunotherapy are more significant in patients with higher CPS scores [12]. The gene discussed is ERBB2; the disease is gastric cancer.