Animal tumor models are often used in experimental designs to study the mechanisms of cancer causation, to examine the effects of modulating factors on the genesis and development of cancer, to assess therapeutic modalities, and to explore possible adverse effects.
Tumor models are specifically used to investigate etiologic and physiopathological properties or processes, especially those which, for obvious practical and ethical reasons, cannot be studied in humans. The ideal animal tumor is histologically similar to the human neoplasm of concern, and latency period, growth, and tendency to metastasize should both be predictable and resemble those of the human neoplasm. The animals should be cost effective, be easily available, and have a genetic uniformity. Variables should be controllable, thereby making it possible to investigate the influence of isolated factors (Davidson, Davis, and Lindsey 1987; Galloway 1989; Weis-burger and Kroes 1994).
For research into matters of nutrition and cancer, chemically induced tumors in animals, predominantly those in rats and mice, are the most important models because they usually best mimic existing types of human cancer (Kroes et al. 1986). For most, if not all, nutrition-related human cancers, tumor model systems are available. They provide an ideal research tool for investigating the influence of individual factors, either in the initiation phase or in the promotion-progression phase of tumor development, or in the overall process.
Possible leads from epidemiological studies can be further investigated in models, thus providing more detailed information, especially regarding risk factors and mechanisms that can be the basis for new epidemiological studies to test a presumed hypothesis. However, animal tumors are only approximations that are rarely identical to human disease. For example, relatively high dosages of genotoxic carcinogens are used to induce the tumor, which tends to distort circumstances when modulating factors are investigated.
Tumor metabolism, growth, potential for and pattern of metastasis, and clinical features can also differ from the human disease. Multiple tumors often occur in models, but seldom in humans. Moreover, the nutrition patterns of experimental animals can be quite distinct from those of humans. Nonetheless, diets can be designed in terms of macro - and micronutrient intake that mimic specific human nutritional traditions.
Animal studies are best understood as providing support for epidemiological studies. It is the integration of results from epidemiological and animal studies that provides the best insight into the etiology and growth of cancer, as well as its treatment, and brings us nearer to the ultimate goal of such research, cancer prevention.
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