This is an intricate issue. Prostanoids help control blood pressure, fight allergies, and modulate inflammation, but too much of them can also lead to increased pain, swelling, and redness in various tissues. In fact, they may be responsible for severe inflammation in many tissues and organs. Fats from fish and vegetable oils are transformed into prostanoids through chemical reactions catalyzed by enzymes named cyclo-oxygenases (COX-1 and COX-2). Now, active COX-2 in benign breast tumors has been connected to a higher risk of developing breast cancer.

Breast biopsies usually neglect non-cancerous but abnormal tissue growth patterns, like atypical hyperplasia. Women with atypical hyperplasia are more prone to breast cancer, but not all of them will develop the disease.

The new study made by a team led by Dr. Lynn Hartmann of the Mayo Clinic in Rochester, Minn., could enable medics to make the difference between precancerous lesions and the ones that will stay benign.

Archival biopsy samples for COX-2 expression were correlated to subsequent breast cancer diagnoses from medical records. The vulnerability to breast cancer was compared with the general population.

235 subjects were diagnosed with atypical hyperplasia between 1967 and 1991. A follow-up of 15 years revealed that 41 women had developed breast cancer.

The likelihood of developing breast cancer rose with the level of COX-2 expression in the initial biopsy sample. For those with the highest level of COX-2 expression, the risk jumped by 5.66 times, from an expected 1.6 cases of breast cancer to nine observed cases.

These results add to other researches showing that COX-2 "may be a relevant target for chemoprevention strategies," the authors write in the "Journal of the National Cancer Institute."

A 2007 research showed that prostanoids made from fish oil are less effective at causing pain and swelling than those made from vegetable oil, and that adding fish oil to the diet decreases the amount of prostanoids made from vegetable oil. Fish oil binds strongly to COX-1, hampering the enzyme's action on vegetable oil, while this affinity does not exist for COX-2, so that a great amount of vegetable oil was still turned into prostanoids.