P-342 Margetuximab combined with anti-PD-1 (MGA012) or anti-PD-1/LAG-3 (MGD013) +/- chemotherapy in first-line therapy of advanced/metastatic HER2+ gastroesophageal junction or gastric cancer

Abstract

Trastuzumab (T), a monoclonal antibody (mAb) targeting HER2, is the standard of care 1st-line therapy for advanced HER2+ GEJ/GC patients (pts). Margetuximab (M), an investigational Fc-engineered anti-HER2 mAb, targets the same HER2 epitope but with higher affinity for both 158V (high binding) and 158F (low binding) alleles of activating Fc receptor CD16A. Data suggests M coordinately enhances both innate and adaptive immunity, including antigen-specific T-cell responses to HER2. PD-1 and LAG-3 are T-cell checkpoint molecules that suppress T-cell function.