The good news is that diet and lifestyle affects the way estrogen is metabolized, so exercising and eating a low-fat diet rich in vegetables may help reduce the risk of breast cancer by altering estrogen breakdown, the study's lead author told Reuters Health.
"We have in our hands a potential avenue for prevention," said Dr. Paola Muti, of the State University of New York at Buffalo.
Before being removed from the body, estrogen has to go through a "metabolic filter" in the liver, Muti explained in an interview. This metabolism of estrogen makes it possible for the hormone to be carried easily through the blood and eventually excreted in urine, she noted.
But the metabolism, or hydroxylation, of estrogen can take place at two different locations on the estrogen molecule, according to Muti. When it takes place at a site called C-16, the process produces "very powerful" estrogen metabolites that can induce biological activity by linking up with cell structures called estrogen receptors, she explained. But when it occurs at the C-2 location, the result is a less active metabolite that can bind to estrogen receptors but without triggering as much biological activity, Muti said.
The extra activity of the C-16 metabolites appears to increase the risk of developing breast cancer, Muti and her colleagues report in the November issue of the journal Epidemiology. In a study of nearly 11,000 healthy Italian women who were followed for about 5 years, premenopausal women who developed breast cancer had a higher percentage of C-16 metabolites in their urine than women who did not develop cancer.
In postmenopausal women, the way estrogen was metabolized did not appear to have an effect on cancer risk, according to the report. However, Muti noted that two other studies have found a connection in older women, so the results do not necessarily rule out the link in postmenopausal women.
The findings are important, Muti explained, because researchers have not had as much luck identifying breast cancer risk factors in younger women as they have in older women. It is too early to say how important a risk factor estrogen metabolism is, but investigators are on the right track, she said.
Of course, any time a potential target for breast cancer prevention is identified, one of the first questions to come to mind is whether a drug can be developed based on the new information. But in Muti's opinion, preventing cancer through lifestyle changes, though often difficult to make, is preferable to a pill. She noted that a combination of exercise and a low-fat diet rich in cruciferous vegetables like cauliflower and broccoli can favorably change the way estrogen is metabolized.