Current international consensus guidelines from the National Comprehensive Cancer Network (NCCN), the European Society for Medical Oncology (ESMO), and Pan-Asian guidelines specify that clinical management of advanced G/GEJ adenocarcinoma requires immunohistochemistry (IHC) and/or molecular testing for Human Epidermal Growth Factor Receptor 2 (HER2/ERBB2) status, mismatch repair (MMR) or microsatellite instability (MSI) status, and Programmed Death-Ligand 1 (PD-L1) expression [13,14,15]. The gene discussed is CD274; the disease is adenocarcinoma.