There’s an environmental link to breast cancer — but chemicals in the air and water may be the least of women’s worries.

A comprehensive study released Wednesday finds that substances to which women voluntarily expose themselves every day — fattening foods, alcohol, cigarettes, oral contraceptives and hormone replacement drugs — are far clearer drivers of risk than industrial chemicals such as bisphenol A and phthalates and a long list of feared additives and environmental pollutants.

The study, “Breast Cancer and the Environment: A Life Course Approach,” was produced by the Institute of Medicine, a panel of independent medical experts most often tapped by government agencies for authoritative advice.

This time, however, the wide-ranging look at possible environmental contributors to breast cancer was requested and paid for — to the tune of about $1 million — by the organization Susan G. Komen for the Cure, the patient advocacy giant that has made pink ribbons synonymous with support for breast cancer research.


Its findings are likely to perturb some environmental advocates, who have warned that the burgeoning industrial use of “endocrine-disrupting chemicals” has set the stage for a plague of breast and other hormone-related cancers in humans.

But though the expert panel concluded that many such chemicals have a “biologically plausible” role in promoting invasive breast cancer, it cautioned that research has so far failed to establish a clear link between these omnipresent chemicals and the new breast tumors found in more than 230,000 women each year in the U.S.

Instead, the team of toxicologists, epidemiologists and clinical cancer experts focused on the immediate role that women’s decisions about diet, exercise, medical care and prescription drugs may have on their risk of developing breast cancer. Although such influences may not fit popular notions of disease-causing environmental factors, the panel defined “environment” in the broadest possible sense, including all the factors other than genes that shape a woman’s health prospects.

Despite many women’s fears of environmental culprits over which they have little control, research linking breast cancer risk to the factors highlighted in the report is far stronger, said breast cancer specialist Dr. Patricia Ganz, who conducts research and clinical work at UCLA’s Jonsson Comprehensive Cancer Center and was not an author of the report.


“Everyone thinks there’s an easy fix, that there was something they put in the drinking water” that can be removed to prevent breast cancer, Ganz said. But the truth about cancer prevention, she said, “is closer to home. … This would be exactly the way I would counsel my patients.”

The report, 20 months in the making, acknowledges there are many unknowns. It calls on the Food and Drug Administration to require better proof from drug makers, before and after market approval, that their products do not increase women’s risk of breast cancer.

It also cites clear evidence that high exposures to ionizing radiation increase breast cancer risk, and says that physicians and patients should carefully weigh the potential benefits of diagnostic imaging scans such as computed tomography, or CT, scans before ordering them. (Because mammograms use low-dose radiation and can help detect tumors, the report’s authors urged women not to avoid them, but to discuss their frequency with a physician.)

And it urges future research to focus on pivotal moments in women’s development — in the womb, at puberty, during childbearing years and at menopause — when even small exposures to suspect chemicals or to everyday choices such as alcohol consumption might have an outsize effect on breast cancer risk.


But the surest ways to drive down breast cancer risk, researchers concluded, lie with women themselves.

The report cites mounting evidence that obesity and body fatness — and particularly weight gain at menopause and after — raise a woman’s risk of developing invasive breast cancer, as well as a welter of research linking breast cancer to a woman’s alcohol consumption, from young adulthood through after menopause, when invasive breast tumors are most likely to appear.

It also notes that numerous studies find exercising drives down a woman’s risk of breast cancer, and that women who use oral contraceptives or hormone replacements containing estrogen and progestin for several years are more likely to develop breast cancer than those who do not.

But after conducting an exhaustive review of suspect chemicals used in industrial, agricultural and consumer-goods manufacture, the panel was far more circumspect.


Though established links do exist for many industrial chemicals, including benzene, ethylene oxide and 1,3-butadiene, risk of any significance appears limited to small numbers of women whose jobs expose them to significant quantities of the chemicals, the report says.

As for other chemicals in wide circulation that are the subject of intense scrutiny and activism — including parabens in cosmetics, growth hormones in livestock, phthalates in plastics and bisphenol A in food and drug packaging — evidence of danger is too scant to recommend avoidance, the panel said.

UC San Francisco’s Robert A. Hiatt, one of the report’s authors, said “the ideal study” would follow a large population of girls and women from before birth to the grave, precisely measuring environmental exposures at every age. But “we can’t really do that efficiently with humans at low cost,” said Hiatt, who is director of population research at the university’s Helen Diller Family Comprehensive Cancer Center.

There may be simpler ways to detect breast cancer hazards that have been overlooked, Hiatt said, including measuring chemical exposures in more precise ways.


The report’s sponsors said the findings pointed the way forward “to gain a full understanding of what substances can be definitively linked to breast cancer.”

Komen for the Cure President Elizabeth Thompson told The Times that the report’s recommendations for future research would be key in guiding the foundation’s $5-million research budget next year.

Despite its focus on life choices, the report may not deflect environmental groups from focusing on synthetic chemicals.

“It is essential to minimize and prevent these exposures,” said Olga Naidenko, senior research scientist for the Washington-based Environmental Working Group.


melissa.healy@latimes.com