Why the dog was ever considered as an appropriate animal for carcinogenicity testing is also not entirely clear... Despite the obvious problems of study design and interpretation, carcinogenicity tests in the dog, lasting 7 years, were requested by regulatory authorities from the late 1960s...One of the best known examples of the inappropriate use of the dog was the carcinogenicity testing of hormonal contraceptives. It is now understood that mammogenesis in the dog is very different from that in primates; quantitative and qualitative differences exist in the feedback control mechanisms, receptor content and behaviour, and target sensitivity and responsivity. As a result of this biological difference there was a high incidence of mammary tumours in long-term studies in dogs treated with progestagens/contraceptive steroids such as lynestrol. Ultimately pressure from the scientific community led, relatively recently, to the requirement for carcinogenicity studies in dogs being dropped.
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Elsewhere, I have pointed out that overfeeding of rats profoundly influences the incidence particularly of endocrine tumours. Furthermore, endocrine tumours and tumours of tissues, such as the breast and uterus, which are very directly under sex-hormone control, constitute a very high proportion of the tumours observed in most carcinogenicity studies in rats. [Comparing] the incidences of tumours in these categories in men and women with those in male and female rats... [shows] the differences between the two species are sufficiently striking to make one wonder how appropriate the laboratory rat is as a model for man in terms of the spectra of tumours to which they are prone.
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We have to think outside the box, inside the Constitution, find ways to do things that will elevate our security, reduce the risk of the incidence of terrorist attack.
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For example, the control incidence of mouse liver tumour varies between 0 and 58% in 41 NTP [National Toxicology Program] bioassays where these tumours are induced by a test chemical.
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The standard carcinogenicity bioassay, which involves treating two rodent species for a minimum of 2 years, at a range of doses, is acknowledged to be an insensitive tool because of the background `noise' of spontaneous disease. Most strains of rat used in such studies have high incidence of pituitary and mammary tumours; some inbred rat strains frequently develop leukaemia or testicular tumours; mice strains show high incidence of malignant lymphomas and liver tumours.
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He who every morning plans the transaction of the day and follows out that plan, carries a thread that will guide him through the maze of the most busy life. But where no plan is laid, where the disposal of time is surrendered merely to the chance of incidence, chaos will soon reign.
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Data from dose-response relationships are sometimes employed to estimate the expected tumour incidence at dose levels very much lower than those which could possibly be employed in conventional [animal] experiments. A number of mathematical models have been employed in such estimates and the results obtained vary considerably. Despite these uncertainties - and the possibly greater ones in extrapolating from animals to man - such models are often employed in some quarters to estimate the likely risk to man.
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Vegetarians have a lower incidence of hypertension than nonvegetarians.
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Incidence of lung and colorectal cancer is lower in vegetarians than in nonvegetarians.
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