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Cancer is one of the main causes of mortality worldwide. Geographical differences in incidence rates suggest a key effect of environmental factors, especially diet, in its aetiology. Epidemiologic and experimental studies have found a role of dietary lipids in cancer, particularly breast, colorectal, and prostate cancers. Their incidence in the Mediterranean countries, where the main source of fat is olive oil, is lower than in other areas of the world. Human studies about the effects of dietary lipids are little conclusive, probably due to methodological issues. On the other hand, experimental data have clearly demonstrated that the influence of dietary fats on cancer depends on the quantity and the type of lipids. Whereas a high intake of n-6 PUFA and saturated fat has tumor-enhancing effects, n-3 PUFA, conjugated linoleic acid and gamma-linolenic acid have inhibitory effects. Data regarding MUFA have not always been conclusive, but high olive oil diets seem to have protective effects. Such effects can be due to oleic acid, the main MUFA in olive oil, and to certain minor compounds such as squalene and phenolic compounds. This work aims to review the current knowledge about the relationship between dietary lipids and cancer, with a special emphasis on olive oil, and the molecular mechanisms underlying these effects: modifications on the carcinogenesis stages, hormonal status, cell membrane structure and function, signal transduction pathways, gene expression, and immune system.

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Breast cancer is the most common cancer among women worldwide. In addition to genetic and endocrine factors, the environment, and specifically dietary habits, plays a key role in the aetiology of this malignancy. Epidemiological and, especially, experimental studies have shown a relationship between dietary lipids and breast cancer although there are conflicting results concerning their potential to modify cancer risk in humans. Abundant data have attributed a potential chemopreventive effect to extra-virgin olive oil (EVOO), the main source of fat in the Mediterranean diet, which is associated with low incidence and mortality rates from cardiovascular disease and some cancers, including that of the breast. It is well-established that the healthy effects of EVOO can be attributed both to its particular fatty acid composition (a high content in oleic acid (OA), a suitable quantity of essential polyunsaturated fatty acids (PUFA) and a relatively low n-6 PUFA/n-3 PUFA ratio) and its richness in minor bioactive compounds such as squalene and phenolic antioxidants. The specific mechanisms by which EVOO and other dietary lipids may exert their modulatory effects on cancer are not fully understood although abundant research has proposed the following: They influence in the stages of the carcinogenesis process, oxidative stress, alteration of the hormonal status, modification of the structure and function of cell membranes, modulation of cell signalling transduction pathways, regulation of gene expression and influence in the immune system. This article will explore the current knowledge of these mechanisms, including our own results in the context of the international literature.

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