(Excerpt below.) "Overall, exposure to mammary gland carcinogens is widespread," the researchers 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 data were too incomplete to estimate how many breast cancer cases might be linked to chemical exposures. 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," they wrote. "If even a small percentage is due to preventable environmental factors, modifying these factors would spare thousands of women." [...] "Almost all of the chemicals were mutagenic, and most caused tumors in multiple organs and species; these characteristics are generally thought to indicate likely carcinogenicity in humans, even at lower exposure levels," they reported. For many of the compounds, the federal government has not used animal breast cancer data when conducting human risk assessments, which are the first step toward regulating chemicals or in setting occupational standards to protect workers. Companies are not required to screen women who work with the chemicals for breast cancer. "Regulators have not paid much attention to potential mammary carcinogens," the researchers wrote.