Follow-up of the population exposed to dioxin after the 1976 accident in Seveso, Italy, was extended to 1996. During the entire observation period, all-cause and all-cancer mortality did not increase. Fifteen years after the accident, mortality among men in high-exposure zones A (804 inhabitants) and B (5,941 inhabitants) increased from all cancers (rate ratio (RR) = 1.3, 95% confidence interval (CI): 1.0, 1.7), rectal cancer (RR = 2.4, 95% CI: 1.2, 4.6), and lung cancer (RR = 1.3, 95% CI: 1.0, 1.7), with no latency-related pattern for rectal or lung cancer. An excess of lymphohemopoietic neoplasms was found in both genders (RR = 1.7, 95% CI: 1.2, 2.5). Hodgkin's disease risk was elevated in the first 10-year observation period (RR = 4.9, 95% CI: 1.5, 16.4), whereas the highest increase for non-Hodgkin's lymphoma (RR = 2.8, 95% CI: 1.1, 7.0) and myeloid leukemia (RR = 3.8, 95% CI: 1.2, 12.5) occurred after 15 years. No soft tissue sarcoma cases were found in these zones (0.8 expected). An overall increase in diabetes was reported, notably among women (RR = 2.4, 95% CI: 1.2, 4.6). Chronic circulatory and respiratory diseases were moderately increased, suggesting a link with accident-related stressors and chemical exposure. Results support evaluation of dioxin as carcinogenic to humans and corroborate the hypotheses of its association with other health outcomes, including cardiovascular- and endocrine-related effects.

The early effects of 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD) exposure in the population involved in the Seveso, Italy, incident in 1976, have been examined in numerous studies. Chloracne was the only effect linked with sufficient certainty to dioxin exposure. The possible longterm consequences were investigated with mortality and cancer incidence studies. Mortality and morbidity findings during the 20-year period following the accident showed increased risk from lymphoemopoietic neoplasm, digestive system cancer (rectum in males, and biliary tract among females, in particular) and respiratory system cancer (lung, among males). In the incidence analyses, also thyroid gland and pleura cancer appeared suggestively increased. Soft tissue sarcomas showed an increase in the largest, yet least exposed, exposure sub-cohort. Several hypotheses associating non-cancer effects with dioxin exposure were corroborated by findings in the Seveso population: this was the case with cardiovascular effects (possibly linked to both chemical exposure and stressful disaster experience), endocrine effects (diabetes among females) and reproductive effects: exposure of men to TCDD was linked to a lowered male/female sex ratio in their offspring. The results of many Seveso studies point to possible gender effects, in accordance with animal models. Notwithstanding the acknowledged study limitations (lack of individual exposure markers, short latency, and small population size for certain cancer types), results of previous experimental and epidemiological studies, along with mechanistic knowledge on dioxin toxicity, support the hypotheses that the observed excesses might be associated with dioxin exposure. The mortality and cancer incidence follow-up of the Seveso cohort are continuing.

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