Abstract 3363: Pharmacodynamic (PD) assessment of drug activity in tumor tissue from patients (pts) enrolled in a Phase I study of MEHD7945A (MEHD), a first-in-class HER3/EGFR dual action antibody, in pts with locally advanced or metastatic epithelial tumors.

Abstract Background Members of the human epidermal growth factor receptor (HER) family of oncogenes are often co-expressed and heterodimerized, suggesting that simultaneous blockade of multiple HER family receptors may be more effective than targeting single receptors. MEHD is a dual-action human IgG1 antibody that can bivalently bind to HER3 and EGFR and block ligand binding to either. FDG-PET imaging is a recognized method of assessing PD modulation with EGFR inhibitors in the clinic. HER3 and EGFR signaling via the MAPK and PI3K pathways can be monitored in tissue by examining phosphorylation of downstream markers. Methods A Phase 1, multicenter, open-label study was conducted to evaluat…