Serum dioxin and cancer in veterans of operation ranch hand

We studied cancer prevalence and exposure to 2,3,7,8-tetrachlorodibenzo-p-d ioxin (dioxin) in veterans of Operation Ranch Hand, the Air Force unit resp onsible for the aerial spraying of herbicides in Vietnam from 1962 to 1971. A comparison group of Air Force veterans who served in Southeast Asia duri ng the same period and who were not involved with spraying herbicides was i ncluded. Comparison veterans were matched to Ranch Hand veterans on age, ra ce, and military occupation. We measured dioxin in 1987 or 1992, extrapolat ed the result to the time of service in Southeast Asia, and assigned each R anch Hand veteran to Background, Low, or High exposure categories. This stu dy had low power to detect an effect for specific or rare cancers. The risk of cancer at sites other than the skin within 20 years of service was incr eased in the Low (odds ratio (OR) = 3.4, 95% confidence interval (CI) 1.5-8 .0) and High (OR = 2.7, 95% CI 0.9-8.0) categories, but the pattern was inc onsistent with another study, suggesting that the excess risk may not have been caused by dioxin exposure. Overall, we found no consistent evidence of a dose-response gradient and no significant increase in cancer risk in the High dioxin exposure category. the subgroup of greatest a priori interest.