Study links dioxin to breast cancer

A 1976 industrial explosion in Seveso, Italy, that spewed dioxin has just been linked to increased incidence of breast cancer. Among women who had lived nearest to the accident site, each 10-fold increase in dioxin exposure–as measured by the carcinogen’s concentration in blood soon after the accident–appears to double breast cancer risk.

This study focused on the most potent dioxin. Called 2,3,7,8-tetrachlorodibenzo(p)dioxin (TCDD), it’s been linked to several human cancers, primarily of the blood and lymph systems. TCDD taints the fat of most people throughout the world. Blood concentrations of TCDD typically run a few parts per trillion. Among many people living near the Seveso accident, blood concentrations spiked to between 10s and 1,000s of parts per trillion.

The new study surveyed breast cancer incidence in 981 women, average age 41. All had been 40 or younger when the accident occurred, had lived near the site, and had accident-era blood concentrations of TCDD available. Fifteen of these women had confirmed breast cancer, report Marcella Warner of the University of California, Berkeley and her colleagues in the July issue of Environmental Health Perspectives. The average age at which breast cancer had appeared was 45, which is younger than expected for this group, the researchers say.

An earlier study that considered Seveso residents who had died failed to find a breast cancer tie to the accident (SN: 9/4/93, p. 149). Warner suspects that that analysis missed the link because it included more older women–who tended to show less exposure to TCDD–and because there hadn’t been enough time for many breast cancers to develop.

She adds that the new results may have little application to populations with far smaller dioxin exposures.

Janet Raloff

Janet Raloff is the editor of Science News for Students, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer.

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