ERBB3 and breast cancer: It also dimerizes with other receptors and activates intracellular signaling through the PI3K/AKT and MAPK/ERK pathways.86 It has emerged as another potential therapeutic target due to 30%-50% expression in breast cancer.87 Patritumab deruxtecan (HER3-DXd) is a monoclonal antibody directed against HER3 bound to the topoisomerase-I inhibitor deruxtecan with a drug-to-antibody ratio of 8.