In the etiology of human cancer the millennia of speculations and the recent decades of unprecedented intensification of controlled investigations have not identified the indisputable cause(s) of any type of the disease. Despite the recent accumulations of overwhelming evidence for the close associations between various environmental (mainly smoking, dietary, cosmic, and sexual) factors and some types of cancer, these associations are, at best, demonstrably causative of the increased cancer-incidence rates rather than of the cancers themselves (Chapter Nine, Section 9.4). These implicated factors are such that they have always involved or are involving most or all of mankind, but among whom only a small proportion is known ever to develop the associated cancers. Moreover, the latter can also develop in the absence of the associations. Bronchogenic carcinoma, for instance, not only develops among some non-smokers but, as such, it is indistinguishable in any material particular from the smokers’ equivalent (Enstrom, 1979; Enstrom and Godley, 1980). Also, the lifetime expectancy of its development among heavy smokers is under 10 per cent. This same principle of the high selectivity of carcinogenic responses among the genetically heterogeneous human population (Chapter Five, Section 5.1) is equally applicable to other human cancer-environmental associations.
KeywordsBreast Cancer Basal Cell Carcinoma Xeroderma Pigmentosum Bronchogenic Carcinoma Dyskeratosis Congenita
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