ERBB3 and breast cancer: High expression and activity of IGF1R and EGFR/HER2 promote TAM resistance and are associated with worse patient outcome in breast cancer.14–18 B6-9 cells with overexpression of PRCP displayed increased IGF1R and ErbB3 signaling and heightened AKT activation in response to heregulin (ErbB3 ligand) and insulin (IGF1R/IR ligand) compared to MCF7.