ERBB2 and breast cancer: To evaluate whether EVOO polyphenols preferentially exhibit tumoricidal effects against HER2-overexpressing breast cancer cells, we further explored both the apoptotic/anti-proliferative effects of EVOO polyphenols in MCF-7 breast cancer cells – which express physiological levels of HER2 (i.e. one single copy of HER2 gene) and in MCF-7 cells stably transduced with pBABE-HER2 or pBABE (empty control) retroviral vectors.