title: The second oncogenic step.
abstract: Three theories of the development of a malignant change which each involve two successive steps are described. Armitage, Doll (1957) proposed that two homologous chromosomes each contained a region which was critical in the control of cell division. The two steps were mutations in these regions brought about by random exposure to carcinogenic agents. Comings (1973) proposed a similar theory but the two steps were considered to be spontaneous mutatons. This paper points out that if one mutation has occurred this can become dominant in at least six ways which mostly involve chromosome translocations. The synergism between oncogenic agents and ionizing radiation and the ability to breed out high and low cancer incidence stocks of animals from a common stock can be explained on the same lines.
mesh_terms: D000818:Animals; D001417:Background Radiation; D002471:Cell Transformation, Neoplastic; D002869:Chromosome Aberrations; D002875:Chromosomes / Q000528:radiation effects; D004171:Diploidy; D004330:Drosophila; D005260:Female; D005796:Genes; D006801:Humans; D008297:Male; D051379:Mice; D009154:Mutation; D009374:Neoplasms, Experimental / Q000209:etiology; D009381:Neoplasms, Radiation-Induced / Q000209:etiology; D010944:Plants; D011123:Polyploidy; D011830:Radiation Effects; D012730:Sex Chromosomes; D014178:Translocation, Genetic