A study comparing the effects of extra-virgin olive oil and corn oil on mammary tumor development in rats has provided detailed information on the different effects of these two oils. Extra-virgin olive oil has been reported to prevent breast cancer, whereas high corn oil diets (rich in omega 6 fatty acids) stimulate it. In the study, mammary tumors were induced by a carcinogen in rats fed either a high extra-virgin olive oil diet, a high corn oil diet, or a control diet. The authors used numerous assays and other tests to characterize the tumors that developed in the rats.

The extra-virgin oil diet was shown to reduce the activity of the oncogene p21Ras, change protein signaling pathways, stimulate tumor cell death, and prevent DNA damage. The p21Ras oncogene promotes uncontrolled cell proliferation and stimulates the growth of tumors. The olive oil diet suppressed the activity of some proteins essential for the survival of cells (the proteins prevent apoptosis, a type of cell death initiated to rid the body of defective and other unwanted cells). Rats on the extra-virgin olive oil diet developed tumors with more benign characteristics compared to the rats on the high corn oil diet. The authors conclude that high extra-virgin olive oil and corn oil diets differently influence breast cancer through a different combination of Ras signaling pathways, a different proliferation-apoptosis balance, and, in all likelihood, different levels of DNA damage.