Influences of environmental chemicals on breast cancer

For millions of women whose lives have been affected by breast cancer, the 1994 discovery of the first breast cancer gene by researchers from the National Institute of Environmental Health Sciences (NIEHS) was a welcome sign of progress in the fight against this dreaded disease. Statistics tell us that breast cancer is still a major health concern for women everywhere. More women in INDIA are living with breast cancer than with any other non-skin cancer. Breast cancer is the leading cause of cancer death for women between the ages of 20 and 59 worldwide.

There is no single cause of breast cancer. Yet understanding the etiology of this complex disease is essential to understand how to prevent it. While 5 to 10 percent of breast cancer cases are thought to be hereditary, the majority of women who develop the disease will never know why. Scientists have identified certain risk factors, like early menstruation and late menopause, alcohol consumption and obesity, but, "most of these risk factors account for very small increases or decreases in a woman's chances of developing breast cancer," according to the National Breast Cancer Coalition.

There has been growing interest in whether environmental factors, including exposures to certain chemicals or changes in lifestyle, may increase the risk of breast cancer. This will include exposures of concern in the home and workplace, and chemicals known to cause mammary (breast tumors) in laboratory animals.

Environmental chemicals may play a role, say some researchers, by damaging DNA, by mimicking hormones that signal tumor cells to grow or by altering mammary gland development early in life. They say the size of the dose may not be what matters most but how early in life and for how long the exposure occurs and to whom; some women may be more susceptible than others. "Breast cancer rates increased enormously over the decades since World War II at the same time that we have had increasing exposure to a wide variety of chemicals and radiation in the environment," says Janet Gray, director of the program in science, technology and society at Vassar College in Poughkeepsie, N.Y., who wrote an extensive review of the research on breast cancer and the environment for the Breast Cancer Fund, an advocacy group in San Francisco, Calif.

"The laboratory evidence is very strong that there are environmental chemicals that affect biological processes linked to breast cancer," says Julia G. Brody, who participated in the review of chemicals and is the executive director of the Silent Spring Institute in Newton, Mass., which researches the environment and women's health. The chemicals include benzene, found in gasoline; polycyclic aromatic hydrocarbons, found in vehicle exhaust, air pollution, tobacco smoke and charred foods; methylene chloride, a common solvent in paint strippers and glues; and some pharmaceuticals, like furosemide, a diuretic and griseofulvin, an anti-fungal.

Most of the 216 chemicals also caused tumors in multiple organs, not just mammary tissue, and in multiple species of animals. "These characteristics are generally believed to indicate likely carcinogenicity in humans," Brody's team reported.

A growing number of studies also implicate endocrine-disrupting compounds (EDCs) - found in certain plastics, pesticides, flame retardants and personal care products - which mimic or block hormones. "There are literally hundreds of studies demonstrating that low doses of endocrine disruptors in early development have profound effects on mammary tissue, breast development and incidence of breast cancer, especially in a variety of rodent models," says Gray.

Instead, some researchers have combed through state environmental data and medical records looking for reliable information. One group found blood samples taken from young women at the time they gave birth, measured their levels of the pesticide DDT, and then followed the women for two decades. Early

exposure to DDT was associated with a fivefold increase in risk of developing breast cancer before age 50. DDT, though banned in 1972, continues to linger in the environment. "That is an important study, and it provides the kind of evidence that is very difficult to get," says Brody.

Four human studies show higher breast cancer risk from exposure to polychlorinated bipheyls (PCBs) in women with a gene mutation that affects how they metabolize these now banned chemicals that were once used in electrical equipment, but still linger.