Abstract
The problem of defining a threshold for even a single carcinogen is both old and new. If one defines “threshold” as the quantity of carcinogen or other etiologic agent just capable of producing a tumor, then at least a common ground is described. However, this “threshold level” may be modulated upwards or downwards in the organism by various environmental and internal factors. A specific case in point is the known influence of dietary fat, especially polyunsaturated fat as an enhancer of many types of tumors, i.e., it appears to be acting to lower the threshold level of carcinogen that is required to elicit a tumorigenic response. Conversely, many dietary antioxidants such as BHT, BHA, and propyl galIate have been shown to effectively raise the threshold level, or decrease the tumorigenic response to a given level of carcinogen. The possible mechanisms through which the dietary factors modify tumorigenesis will be discussed. These will include specific influences and interactions of dietary factors on 7, 12-dimethylbenz(a) anthracene-induced mammary car-cinogenesis, carcinogen uptake and retention by the target tissue, as well as influences on glandular development which may result in an alteration of the number of possible “targets” available at the time of carcinogen exposure.