Olive oil as a naturally-occurring "anti-HER2 cocktail". In terms of protective effects against breast cancer, olive oil exhibits a very favorable fat composition as it appears to unite a new composite biomarker for breast cancer,i.e., a low ω-6/ω-3 PUFA ratio and elevated ω-9 MUFA levels. We previously demonstrated that ω-3 PUFAs such as alpha-linolenic acid (ALA) and docosahexaenoic acid (DHA) as well as the ω-9 MUFA oleic acid (OA) significantly inhibit HER2 expression and HER2-driven oncogenic activity in breast cancer cells naturally exhibiting HER2 gene amplification and HER2 protein overexpression [9, 11, 19-21, 81, 82]. Conversely, the ω-6 PUFA linoleic acid (LA) was found to significantly activate and up-regulate HER2. Since HER2 plays a pivotal role in malignant transformation, tumorigenesis, metastasis, and treatment failure in breast cancer disease, our current findings showing that blockade of HER2 expression and HER2-driven oncogenic activity also represents a new molecular mechanism of quantitatively minor phenolic components of olive oil such as oleuropein and hydroxytyrosol (OH-Tyr) strongly support the notion that olive oil may be extremely efficient at inhibiting HER2-regulated breast cancer etiology and metastatic progression.