Increased consumption of omega-6 fatty acids, found in corn oil and most of the oils used in bakery products, could be a reason for the rise in incidence of prostate cancer in recent years, say the researchers.
In a previous study, Dr Millie Hughes-Fulford, director of the Laboratory of Cell Growth at the San Francisco VA Medical Center (SFVAMC) and colleagues introduced arachidonic acid, an omega-6, into human prostate tumor cells in culture. They found that they caused the production of the enzyme cPLA2, which in turn caused a chain of biochemical reactions that led to tumor growth.
Their latest research builds on these earlier findings, revealing that the fatty acids trigger this "biochemical cascade" by turning on a gene signaling pathway that leads directly to tumor growth.
"After we added omega-6 fatty acids to the growth medium in the dish, and only omega-6, we observed that tumors grew twice as fast as those without omega-6," said Hughes-Fulford.
"Investigating the reasons for this rapid growth, we discovered that the omega-6 was turning on a dozen inflammatory genes that are known to be important in cancer. We then asked what was turning on those genes, and found that omega-6 fatty acids actually turn on a signal pathway called PI3-kinase that is known to be a key player in cancer," she added.
This is not the first time that scientists have connected this group of fatty acids to cancer. Omega-6 fats have also been linked to the development of breast cancer, with a Spanish team reporting in 2004 that the fats enhanced expression of certain genes that accelerate the disease.
And because of the increased levels of omega-6 fatty acids in the modern American diet, Hughes-Fulford says the latest study is significant in examining the possible link between diet and prostate cancer.
Around 60 years ago, the dietary ratio of omega-6 to omega-3 in the US was one to two. Today, the ratio is 25 to one. Over that same 60 years, the incidence of prostate cancer in the US has increased steadily, say the study authors.
Hughes-Fulford is currently continuing her research by conducting tests on animals fed with different levels of omega-3 and omega-6 fatty acids, to observe how the tumors grow in animals.