Several epidemiological studies of phenoxy herbicide and chlorophenol producers found increases in cancer mortality in populations exposed to 2,3,7,8TCDD. Exposure to this compound has been especially associated with the development of softtissue sarcoma after a prolonged latency period. The human data suggest that 2,3,7,8TCDD may be a human carcinogen, however, the interpretation of many of these studies is limited by confounding factors (e.g., small cohorts, short latency periods, coexposure to other chemicals, inadequate exposure data). There are no reliable human studies on the carcinogenicity of other PCDDs. Animal studies provided sufficient evidence that 2,3,7,8TCDD is a carcinogen after oral and dermal exposure. Furthermore, 2,3,7,8TCDD has promoting ability on tumours initiated by diethylnitrosourea. Similarly, chronic oral exposure of rodents to a mixture of 1,2,3,6,7,8HxCDD and 1,2,3,7,8,9HxCDD or to 2,7DCDD resulted in carcinogenic effects.
No studies were located regarding cancer effects in animals following inhalation exposure to PCDDs.