Invited Commentary: How Do the Seveso Findings Affect Conclusions Concerning TCDD as a Human Carcinogen?

Abstract

Dioxin, specifically 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), is a chemical with remarkable persistence in humans and a half-life of about 5–10 years. It is also noteworthy that a recent International Agency for Research on Cancer (IARC) monograph classified TCDD as a group 1 human carcinogen, in spite of the conclusion by the Working Group involved that there was only “limited evidence” of carcinogenicity in epidemiologic studies (1). The key epidemiologic evidence came from four industrial cohort studies (2 –5), each of which included confirmation of exposure for some workers with measurements of the concentrations of TCDD in their blood or fat samples. Overall increases in mortality from all cancers combined were reported for each of these cohorts, but no particular cancer sites were prominent. This IARC monograph stated that the “lack of precedent for a multi-site carcinogen without particular sites predominating means that the epidemiological findings must be treated with caution” (1, p. 337).