Pesticides and breast cancer.

About 14 percent of all Danish women develop breast cancer, a rate that has more than doubled since the late 1960s. A new study finds that exposure to a few chlorinated pesticides might be contributing to the cancer's rise.

Annette P. Hoyer of the Copenhagen Center for Prospective Population Studies and her colleagues measured blood concentrations of chlorinated compounds commonly found stored in body fat: 18 pesticides (or their breakdown products) and 28 polychlorinated biphenyls. The blood samples came from 240 area women with breast cancer and some 480 others who remained cancerfree. All were participants in the Copenhagen City Heart Study, which had collected the blood 17 years earlier, before any cancers had appeared.

Even after accounting for well-known breast-cancer risks, such as a woman having no full-term pregnancies, blood concentrations of two pesticides emerged as independent risks for the malignancy, Hoyer's group reports in the Dec. 5, 1998 Lancet.

A woman's chance of developing the cancer edged up slightly with increasing blood concentrations of beta-hexachlorocyclohexane, a constituent of the toxic pesticide lindane (SN: 3/15/97, p. 157). The persistent insecticide dieldrin, banned in the United States, provoked a more dramatic increase. Women with the highest blood concentrations of this estrogen-mimicking pollutant faced more than double the breast-cancer risk of those whose blood carried little or no dieldrin.

The good news: The researchers found no link between the cancer and any of the other pollutants in the study--including DDT, chlordane, and kepone--all of which accumulate in body fat.