Breast cancer linked to chemicals

Reduced exposure to common products may prevent disease

May 14, 2007|By Marla Cone | Marla Cone,LOS ANGELES TIMES

More than 200 chemicals -- many found in urban air and everyday consumer products -- caused breast cancer in animal tests, according to a compilation of scientific reports published today.

Writing in a publication of the American Cancer Society, researchers said that reducing exposure to the compounds could prevent many women from developing the disease. The research team from five institutions analyzed a growing body of evidence that links environmental contaminants to breast cancer, the leading killer of U.S. women in their late 30s to early 50s.

Experts say that family history and genes are responsible for a small percentage of breast cancer cases but that environmental or lifestyle factors such as diet are probably involved in the vast majority.

"Overall, exposure to mammary gland carcinogens is widespread," researchers from institutions in the Boston area, Los Angeles and Buffalo, N.Y., wrote in a special supplement to the journal Cancer. "These compounds are widely detected in human tissues and in environments, such as homes, where women spend time."

The scientists said there is insufficient data to estimate the number of breast cancer cases linked to chemical exposure. But, because the disease is so common and the chemicals so widespread, "the public health impacts of reducing exposures would be profound even if the true relative risks are modest. If even a small percentage is due to preventable environmental factors, modifying these factors would spare thousands of women."

The three reports and a commentary were compiled by researchers from the Silent Spring Institute, a women's environmental health institute in Newton, Mass.; Harvard's Medical School and School of Public Health; the Roswell Park Cancer Institute; and the University of Southern California's Keck School of Medicine. Silent Spring Institute Executive Director Julia Brody led the team.

In response to the findings, Susan G. Komen for the Cure, a breast cancer prevention group that funded the work, pledged $5 million more for developing improved research tools to root out environmental causes.

Reviewing hundreds of studies and databases, the team produced what it called "the most comprehensive compilation to date of chemicals identified as mammary carcinogens."

They named 216 chemicals that induce breast tumors in animals. Of those, people are highly exposed to 97, including industrial solvents, pesticides, dyes, gasoline and diesel exhaust compounds, cosmetics ingredients, hormones, pharmaceuticals, radiation and a chemical in chlorinated water.

"Almost all of the chemicals were mutagenic, and most caused tumors in multiple organs and species," they wrote.

For many of the compounds, the federal government has not used the animal data when conducting human risk assessments, which are the first step toward regulating chemicals, or in setting occupational standards to protect workers.

Toxicologists say that mammals such as rats and mice often develop the same tumors as humans, and that animal tests are efficient means of testing the effects of chemicals.

Ana Soto, a Tufts University professor of cell biology who specializes in cellular origins of cancer and effects of hormone-disrupting contaminants, said there probably is a link between breast cancer and exposure to chemicals in the environment, particularly early in life. "It's a very likely, very plausible hypothesis," said Soto, who did not participate in the new studies. "More and more, cancer looks like an environmental disease."

Twenty-nine of the breast carcinogens are produced in volumes exceeding 1 million pounds annually in the United States. Seventy-three are in consumer products, such as 1,4-dioxane in shampoos, or are food contaminants, such as acrylamide in french fries. Thirty-five are common air pollutants, 25 are in workplaces where at least 5,000 women are employed, and 10 are food additives, according to the reports.

There are probably many more than 216, the researchers said, because only about 1,000 of the 80,000 chemicals registered for use in the United States have been tested on animals to see whether they induce cancerous tumors or mutate DNA. Such tests cost $2 million each.

Because epidemiological studies are difficult and full of uncertainties, human data "is still relatively sparse," the researchers wrote. Only 152 studies have examined whether women exposed to contaminants are more likely to have breast cancer -- compared with nearly 1,500 that have explored the links between diet and the disease -- and most of the 216 carcinogens were not included.

"Despite this large remaining gap, research in the last five years has strengthened the human evidence that environmental pollutants play a role in breast cancer risk," the researchers wrote. They said the existing studies suggested "substantial public health impact."

Human evidence is particularly strong for PCBs -- compounds widely used in the 1940s to late 1970s that still contaminate fish and other foods -- and for polycyclic aromatic hydrocarbons, or PAHs, found in exhaust of diesel vehicles and gasoline-powered cars. Solvents in dry cleaning, aircraft maintenance and other jobs also seem to increase breast cancer rates.

The scientists hope to lay the groundwork for new human studies and to persuade officials to use existing animal data to strengthen regulations and require more testing of chemicals.

Emerging evidence suggests that the roots of breast cancer come early in life, and more animal and human research should focus on that, said Patricia Hunt, a professor at Washington State University.

Marla Cone writes for the Los Angeles Times.

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