Second, when using human breast cancer-derived in vitro models naturally exhibiting HER2 gene amplification and HER2 protein overexpression, exogenous supplementation with physiological concentrations of oleic acid (OA; 18:1n-9) – the main ω-9 monounsaturated fatty acid (MUFA) in EVOO – was found to drastically suppress the expression of HER2 and to synergistically enhance both the growth-inhibitory and the HER2 down-regulatory effects of the monoclonal antibody trastuzumab (HerceptinTM) [15-17]. The gene discussed is ERBB2; the disease is breast cancer.