Human Epidermal Growth Factor Receptor-2 Gastric Adenocarcinoma: Expanding Therapy of a Recognized Target

Simple Summary Human epidermal growth factor receptor-2 (HER2) is a well-known target for approximately 15% of gastric adenocarcinomas (GACs). Although a plethora of HER2-targeted agents are marketed, currently only two agents are approved for GAC. These two agents are used only in the metastatic setting. Trastuzumab is utilized in combination with front-line chemotherapy, and trastuzumab deruxtecan is given following failure of trastuzumab therapy. Questions remain as to why HER2 biology is different in different tumor types. Here, we discuss past HER2-targeted failures, resistance patterns, and new agents on the investigative horizon.Abstract Human epidermal growth factor receptor-2 (HER2) is a well-known cancer target. Many HER2-targeted agents are marketed and being investigated. Unfortunately, these therapies lack consistent responses and outcomes amongst different tumors. Questions remain as to why HER2 biology is different in different tumor types. Gastric adenocarcinomas (GACs) demonstrate both intra- and inter-tumor HER2 expression heterogeneity and show discordance amongst primary and metastatic disease sites. This creates barriers in determining HER2 agents' effectiveness and contributes to the failure of some HER2-targeted agents in the treatment of HER2-positive advanced GACs. Trastuzumab deruxtecan, an antibody drug conjugate of trastuzumab with a topoisomerase inhibitor, was recently approved for the treatment of refractory HER2-positive advanced GAC patients. There are exciting and newer therapies under investigation. Examining resistance patterns (both adaptive and acquired) along with establishing a better understanding of the intra- and inter-tumor heterogeneity is necessary to ensure successful progress. Here we review the current status of HER2-targeted therapy in GACs. We additionally review newer therapies under investigation and their potential role in HER2 GACs.