High doses of fish oil quickly change the fatty acids in 
women's breast tissue in a way that might lower breast 
cancer risk, suggests a preliminary study out Wednesday.

But the findings, in 25 women who have had breast cancer, 
don't yet prove fish oil can prevent the disease or its 
recurrence, says oncologist John Glaspy, UCLA Medical School.

The report, in the Journal of the National Cancer Institute, 
shows breast tissue changes three months after a diet shift. 
Taking 3 grams of fish oil a day - about the same as eating 
two large salmon - spurred a four-fold increase in the ratio 
of omega-3 to omega-6 acids in the blood, and a 1.4-fold
rise in the ratio in breast tissue. "There's a biological reason 
to think this will lower breast cancer risk," Glaspy says.

Japanese women, whose breast cancer rate is much lower 
than Americans', have a high ratio of omega-3 to omega-6 in 
their breasts. When they move to the USA and adopt its diet, 
their breast cancer rate equals that of U.S. women within a 
generation.

Studies show women with breast cancer have a two- to 
five-fold higher ratio of omega-6 to omega-3, Glaspy says. 
In animal studies, omega-6 has been shown to promote 
tumor growth, omega-3 to inhibit it.

Longer, larger studies are needed to prove a benefit, Glaspy 
says. He's tracking 150 women for several years. Also, 
long-term large doses of fish oil aren't proven safe.

Marc Lippman, a breast cancer expert at Georgetown 
Medical School, Washington, calls it "highly overstated" to link 
fatty acid ratios to breast cancer risk. Most risk is due to 
reproductive history, genetics and other factors over which 
women have little control, he says.