As of 2021, it was established that three molecular biomarkers predict response to targeted therapies in gastric and gastroesophageal junction (G/GEJ) cancer: HER2 positivity for trastuzumab and trastuzumab deruxtecan, and PD-L1 expression for pembrolizumab and microsatellite instability (MSI) status (22). The gene discussed is ERBB2; the disease is cancer.