BETHESDA, MarylandResults from the largest epidemiologic investigation of possible links between two major types of environmental pollutants and breast cancer indicate a 50% increase in risk of the disease for women exposed to polycyclic aromatic hydrocarbons (PAHs) at the highest level. However, researchers failed to find an association between organochlorine compounds, which include DDT, and an increased risk of breast cancer.
The new findings emerged from two studies conducted as part of the Long Island Breast Cancer Study Project, which Congress mandated in 1993. The two studies involved a total of 1,058 women living in Nassau and Suffolk counties on Long Island, which have disproportionately high breast cancer rates, compared with other counties in New York State.
The goal of the two population-based, case-control studies "was to determine whether breast cancer incidence in these two counties was associated with exposures to environmental contaminants," said Marilie D. Gammon, PhD, who served as principal investigator for both studies. "What we observed did not support that possibility strongly." Dr. Gammon is associate professor of epidemiology, University of North Carolina School of Public Health, Chapel Hill.
PAHs result from incomplete combustion. They are inhaled with such things as cigarette smoke and from the smoke and vehicle exhaust that result from burning fossil fuels, and are ingested by eating grilled and smoked foods.
The compounds are potent mammary carcinogens in rodents, and the federal government has designated several of them as probable or possible human carcinogens. However, researchers have not clearly demonstrated carcinogenic effects in the breasts of women.
Organochlorines include several pesticides (such as DDT); the family of industrial compounds known as PCBs; and the termiticide chlordane. DDT was used widely on Long Island to control mosquitoes and gypsy moths before it was banned in 1972. Several previous epidemiologic studies have indicated a link between organochlorine exposure and breast cancer. However, most such studies have not supported an association of DDT and PCBs with the disease.
In the PAH study, Dr. Gammon and her colleagues focused on PAH-DNA adductsplaces where the hydrocarbon attaches to the DNA in cells. Adducts serve as markers for exposure to a chemical and are widely believed to indicate tissue damage. The researchers looked for adducts in cells from blood samples donated by 576 women newly diagnosed with breast cancer and 427 women without breast cancer who served as controls.