SAN ANTONIO - Women concerned about breast cancer should worry less about cellphones and hair dyes and worry more about weighing or drinking too much, exercising too little, using menopause hormones and getting too much radiation from medical tests. So says a new report on environmental risks by a respected panel of science advisers.

By environment they mean everything not governed by genes -- what's in the air and water but also diets, vitamin use and even things like working night shifts.

And while they lament that most chemicals in consumer goods get little safety testing, they find too few studies in people to say whether there is a breast cancer risk from certain pesticides, cosmetics or bisphenol A, known as BPA and used in many plastics and canned food liners, although it has been eliminated from baby bottles and many reusable beverage containers in recent years.

"We don't have enough data to say 'toss your water bottles,"' said Irva Hertz-Picciotto, chief of environmental and occupational health at the University of California, Davis.

She headed the Institute of Medicine panel -- independent experts under the National Academy of Sciences who advise the government and others. This report was paid for by Susan G. Komen for the Cure, a breast cancer foundation. It was presented Wednesday at a cancer conference in Texas.

We've done a better job of treating breast cancer than preventing it, said Dr. Michael Thun, senior epidemiologist for the American Cancer Society, who helped review the report. Breast cancer death rates in the U.S. fell 31 per cent from 1990 to 2007, but incidence rates declined only about five per cent.

Weight and obesity matter because fat cells make estrogen, and that hormone fuels the growth of most breast cancers, he said.

Other factors are more complex. Moderate alcohol consumption may lower the risk of heart disease but seems to raise the risk of breast cancer a little.

The report sorts the evidence for higher breast cancer risk factors like this:

  • Yes: Hormone therapy combining estrogen and progestin, excess weight after menopause, alcohol consumption and radiation from too many medical tests, especially during childhood. The panel doesn't say how much radiation is too much, but says two or three abdominal CT scans give as much as atomic bomb survivors received. Mammograms use minuscule amounts and should not be avoided. Oral contraceptives slightly raise breast cancer risk while taken, although cancer rates are very low in the age groups that use them.
  • No: Hair dyes and the kind of radiation from cellphones, microwaves and electronic gadgets.
  • Probable: Smoking.
  • Possible: Secondhand smoke, nighttime shift work and exposure to benzene and a couple other chemicals through jobs or from breathing car fumes or pumping gas. It is "biologically plausible" that BPA and certain other plastics ingredients might affect estrogen, which fuels most breast cancers, but evidence is mostly in animals and lab tests -- not enough to judge whether they harm people, the panel concluded.

"There's a tremendous desire to blame someone or something" for breast cancer, said Dr. Eric Winer, a cancer specialist at Dana-Farber Cancer Institute in Boston and chief scientific adviser to the Komen foundation.

"There's a real danger in prematurely concluding that a substance is the culprit and then closing your eyes and not paying attention to what might be a much more concerning factor," or substituting something for BPA that might be worse, he said.

Thun of the cancer society agreed.

"One should first do everything possible to address the known risk factors," he said. "If I'm making the choices, I wouldn't put this (BPA) at the top of my list."

However, Laura Anderko, a Georgetown University Medical Center public health scientist, said she was "deeply disappointed" by the report's heavy emphasis on personal responsibility for cancer prevention.

"It is in stark contrast to the President's Cancer Panel report last year that has a strong call to action on chemical policy reform," she wrote in an email.

About 230,000 cases of breast cancer are expected to be diagnosed this year in the U.S. Less than 10 per cent of cases are due to inherited genes.