The mode of carcinogenic action of saccharin

Role of epidemiology in health risk assessment

Human health risk assessment has been the object of systematic study in recent years, with formal models of risk assessment and risk management having been proposed by several national and international health agencies. The particular model developed by the Environmental Health Directorate of Health and Welfare Canada was examined in some detail and used to focus on the role of epidemiology in the overall process of risk assessment. In addition to providing information fundamental to the identification of environmental carcinogens and the estimation of carcinogenic risks, epidemiology may also play a role in shaping risk perception and in improving risk communication practices. Taken collectively, epidemiologic data on health risks provide a basis for improved disease surveillance and prioritization of public health concerns. Both descriptive and analytic epidemiologic protocols may be used to gather information on disease etiology. Because of the potential for bias and confounding in observational studies of human populations, epidemiological data should be subjected to careful evaluation in accordance with established criteria before a causal relationship between exposure and disease is inferred. Toxicological studies using nonhuman test systems may be used to avoid these problems, but at the expense of obtaining indirect information on human health risks. Nonetheless, toxicological data provide an important complement to epidemiological data, providing information on potential health risks in advance of human exposure and offering a means of indirectly assessing risks in situations where human studies fail to provide informative results. The complementary roles of epidemiology and toxicology in health risk assessment were examined using four case studies. While the epidemiological evidence linking tobacco consumption to lung cancer is now unequivocal, the corresponding data on involuntary smoking, although strongly suggestive of increasing the relative risk of lung cancer, requires further confirmation before providing the same degree of evidence as now exists for active smoking. At present, the best estimates suggest that overall mortality attributable to active smoking may exceed that due to passive smoking by roughly 100-fold. Despite this large difference in health impact, passive smoking continues to be the focus of much public concern, in part because of the involuntary nature of the risk involved. Because of the abundance of good epidemiological data on tobacco, toxicology has assumed a secondary role in defining the health risks associated with smoking. In contrast, while epidemiological studies with saccharin and formaldehyde have provided unequivocal evidence of carcinogenic effects in animals exposed to high doses, thereby raising concerns over potential human carcinogenicity.(ABSTRACT TRUNCATED AT 400 WORDS)

International Commission for Protection against Environmental Mutagens and Carcinogens. ICPEMC publication No. 13. The need for biological risk assessment in reaching decisions about carcinogens

The prudent assumption that carcinogen bioassays in rodents predict for human carcinogenicity is examined. It is suggested that in certain cases, as for example the induction of tumors against a high incidence in controls, or in situations in which high dose toxicity may be a critical factor in the induction of cancer, the probability that animal bioassays predict for humans may be low. The term 'biological risk assessment' is introduced to describe that part of risk assessment concerned with the relevance of specific animal results to the induction of human cancer. Biological risk assessment, which is almost entirely dependent on an understanding of carcinogenesis mechanisms, is an important addition to present mathematical modeling used to predict the effects of animal carcinogens that have been demonstrated after high dose exposure, to the effects of the much smaller doses to which humans are perceived to be exposed. Evidence for the conclusions reached by biological risk assessment may sometimes be supported by a careful review of human epidemiological data.

Carcinogenesis of 4-aminobiphenyl in BALB/cStCrlfC3Hf/Nctr mice

Male and female (840 each) BALB/cStCrlfC3Hf/Nctr mice were given 0, 7, 14, 28, 55, 110 and 220, and 0, 7, 19, 38, 75, 150 and 300 ppm, respectively, of 4-aminobiphenyl in their drinking water. Necropsies on killed animals were performed at 13, 26, 39, 52 and 96 weeks on dose. Dose-related neoplasms were angiosarcomas, bladder urothelial carcinomas and hepatocellular neoplasms. The non-neoplastic dose-related lesions were left atrial thrombosis, bladder urothelial hyperplasia, splenic hemosiderosis and splenic erythropoiesis. The incidences of bladder carcinoma and atrial thrombosis were higher in the males and the incidences of hepatocellular neoplasms and angiosarcomas were higher in the females.

Dose relationships in experimental carcinogenesis: dependence on multiple factors including biotransformation

The probability of obtaining a tumor in a carcinogenesis bioassay depends mainly on the time on test and on the dose of carcinogen used. There is very limited data on the shape of this surface or reliable data on dose-response or time on test-response relationships. Ullrich's data on tumor induction by low dose radiation shows a variety of shapes of curve depending on the tissue chosen for investigation. As radiation probably does not concern the processes involved in xenobiotic metabolism, these observations clearly demonstrate that factors other than metabolism are important. An attempt is made to discuss the shape of the dose-response curve in relation to a number of factors including the background incidence of tumors in a tissue, mechanisms of "nongenotoxic" or toxicity-related carcinogenesis, and xenobiotic activation of carcinogens.