(USA TODAY) -- When Heather Rogers was diagnosed with breast cancer three years ago, she asked herself, "Why me?"
Like 90% of women with the disease, Rogers had no family history of breast cancer. She was healthy, only 46, never considered herself at high risk.
And like many breast cancer survivors, she wonders if her disease was caused by chemicals in the environment.
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Rogers says she's frustrated that doctors are unable to give her a clear answer.
"They've made a lot of progress, which I'm really grateful for," says Rogers, of Alexandria, Va. "But I was surprised that, after all these years, there are still so many unanswered questions."
Although the American Cancer Society estimates that environmental pollution causes 6% of all cancer deaths - or about 34,000 lost lives each year - the group doesn't offer specific advice on which chemicals to avoid to reduce breast cancer risk.
Difficult to ascertain
To some extent, scientists will never have "definitive" answers, says Julia Brody of Silent Spring Institute, an advocacy group that studies breast cancer and the environment.
People are exposed to a countless mix of chemicals over a lifetime. Since cancers usually take decades to develop, it can be hard to make clear connections. And since researchers can't test toxins on humans, they rely on studies in animals and lab dishes, as well as observations of population trends, Brody says.
Scientists sometimes disagree about how to interpret the results. Even more crucially, though, experts disagree about how to act in the face of uncertainty.
Some cancer experts, such as the American Cancer Society's Michael Thun, says it's important to make health recommendations only when doctors can be very sure about the science.
"The problem with sounding too many alarms is that people can't tell what's real," he says.
Exercise caution to reduce exposure
Other medical leaders, such as the President's Cancer Panel and the Endocrine Society, follow the "precautionary principle," arguing that it makes sense to reduce exposures to chemicals that appear harmful. In a May report, the cancer panel urged the country to act to protect people from "grievous harm" caused by toxins. And in a 2009 report, the Endocrine Society warned that hormone-disrupting chemicals in consumer products may contribute to cancer, infertility and other conditions.
Doctors expect to get many answers from the National Children's Study, launched this year, which will follow 100,000 children from birth - or earlier - through age 21. Researchers will study chemicals in blood, urine and even umbilical cords, looking for links to cancer, asthma, autism and other disorders.
But Brody says that Americans don't need to wait for that study's results to begin protecting themselves and their children. More than 200 chemicals have been linked to breast cancer in animals, she says.
A growing number of scientists are particularly concerned about chemicals that alter natural hormonal systems. These chemicals don't need to cause genetic mutations to cause breast cancer, says Janet Gray, a professor at New York's Vassar College.
Toxins could increase the number of new cancers by pushing girls into early puberty - a known risk factor for breast tumors, Gray says. Such "hormone-disrupting" chemicals are everywhere - plastics, pesticides, even perfumes.
"We believe there's enough science to act now," says Janet Nudelman of the Breast Cancer Fund.
TAKE STEPS TO CUT YOUR RISK
While doctors are still trying to understand what causes breast cancer, experts say there are a number of proven ways for women to reduce their risk.
Maintain a healthy weight. Obesity has been linked to various cancers.
Limit alcohol consumption. Alcohol has been linked to an increased risk of breast cancer.
Reduce unnecessary radiation exposure, such as from CT scans.
Avoid or limit use of hormone replacement therapy. Long-term use has been linked to ovarian and breast cancer.
Have your first child before age 30.
Breast-feed as long as possible.
If you're at high risk -- for instance, you have several close relatives with the disease -- talk to your doctor about breast cancer medications such as tamoxifen or raloxifene.
Source: American Cancer Society