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Abstract:
Cancer causation in humans is at least a three-dimensional problem too often viewed from only two dimensions, especially as far as the two-dimensional results (dose versus response) of cancer induction tests in animals are viewed. The expression of a cancer represents a critical convergence of additional factors in the third dimension which include metabolic variables, many of which may involve secondary mechanisms. Many of these mechanisms are involved in the causation pattern of cancer in humans and can be expected to operate within the dose-response considerations observed in the fields of toxicology and pharmacology. The expression of critical reactions of cells in relatively unprotected tissues may occur more readily after exposures involving fewer molecules of one "carcinogen" as compared to another "carcinogen". Results from animal tests may have limited human relevance in some instances and detract us from consideration of the more fundamental factors involved in the etiology of human cancer. A precipitous rush to "zero tolerances" for all animal carcinogens may impair our efforts to prevent the worst "causes" of cancer induction in humans.