ERBB2 and breast cancer: Interestingly, EGFR and HER-2 coexpression in breast cancer was recently associated with reduced overall survival (OS) and disease-free survival (DFS).31 It is also increasingly clear that the high cell-surface HER-2 density that accompanies gene amplification alters the normal equilibrium of EGFR dimers in favor of HER-2 containing heterodimers, thus altering ligand dependant signaling mechanisms.