WEDNESDAY, March 19 (HealthDay News) -- In the decades following World War II, both breast cancer rates and the use of synthetic chemicals soared in the United States -- and a new report contends there's a strong connection between the two.

Produced by the Breast Cancer Fund, a non-profit group whose mission is to identify environmental links to breast cancer, The State of the Evidence: 2008 concludes toxic chemicals in the environment, along with increased radiation exposure, are the main culprits in the sharp rise of breast cancer incidence.

The report cautions that "in-utero" [in the womb] and early childhood exposure to carcinogens through plasticizers, estrogen-mimicking substances and other chemicals may increase the risk of breast cancer in adult life.

"As we looked at the research comprehensively, the themes of interactions of timing and mixtures of chemical exposures and also radiation exposure as risks emerged. In bringing this broad focus to environmental causes of breast cancer, we hope to find ways to lower the future incidence of breast cancer not only for adults but, most importantly, for our children and grandchildren," said Dr. Janet Gray, an endocrinology researcher at Vassar College, who edited the report.

However, some public health experts say there's no scientific proof establishing a link between environmental contaminants and breast cancer.

Based on a review of more than 400 breast cancer studies, The State of the Evidence noted that more than 80,000 synthetic chemicals are currently used in the United States, although complete toxicological screening data are available for only 7 percent of them. Many of these substances are known to remain in the environment for many years and accumulate in body fat and breast tissue.

One group of chemicals -- phthalates, which the Breast Cancer Fund report identifies as a breast cancer risk -- was in the news last week when the U.S. Senate passed legislation strengthening the Consumer Product Safety Commission with an amendment requiring all children's toys and child-care products to be free of these hormone system disruptors. A study by Fox Chase Cancer Center in Philadelphia last year found that phthalates accelerated breast development and genetic changes in newborn female lab rats, a condition that might predispose the animals to breast cancer later in life.

Exposure to chemicals that mimic estrogens in the body, called xenoestrogens, is thought to be the reason more girls are entering puberty at younger ages, according to Jeanne Rizzo, executive director of the Breast Cancer Fund.

In addition to phthalates, the new report lists other endocrine-disrupting compounds that the study authors say have been shown to affect the risk for breast cancer in humans, or the risk of mammary cancer in animals. Those compounds, according to the report, include:

• Pesticides such as DDT, dieldrin, aldrin and heptachlor; triazine herbicides
• Bisphenol, a chemical used to make plastics, epoxy resins and dental sealants
• Polyaromatic hydrocarbons (byproducts of combustion)
• Tobacco smoke
• Dioxins
• Alkyphenols (industrial chemicals used in cleaning products)
• Metals including copper, cobalt, nickel and lead
• Parabens (anti-microbials used in personal care products)
• Food additives such as compounds given to cattle and sheep to enhance growth

The report also cites environmental factors that may exert cancer-causing effects without hormone disruption. Those factors include exposure to the petrochemical solvent benzene; organic solvents used in the computer, furniture and textile industries; polyvinyl chloride (PVC) used in a variety of appliances, food packages and medical products; 1,3-butadiene, a byproduct of petroleum refining and vehicle exhaust; ethylene oxide, used in medicine and some cosmetics; and aromatic amines, byproducts of manufacturing plastics and dyes. Both ionizing and non-ionizing radiation are also listed as suspected cancer-causing agents, the report stated.

"The conclusions of the surveyed research show us we need to look earlier and earlier at the impact of chemical exposure in utero and early life and how toxins, radiation, genetic predisposition, diet, exercise and all those things interact together to increase breast cancer risk. The results of this study compel us to look at the need for broad public health policy reform and more federally funded research," Rizzo said.

In response to the report, Tiffany Harrington, public affairs director with the American Chemistry Council, said the chemical industry is seeking to better understand the complex relationship between modern chemistry and human health.

"The chemistry industry has contributed to endocrine research by supporting applied scientific studies focused on developing the datasets needed to evaluate the reliability of endocrine screening methods," she said.

Meanwhile, environmental medicine expert Dr. Jonathan Borak, an associate clinical professor of medicine at Yale University's School of Medicine, said a host of studies have found no clear link between specific toxins and breast cancer.

"So far, I have not seen any compelling evidence of a link between any environmental contaminants and breast cancer," he said.

More information

For more on breast cancer, visit the American Cancer Society.