Two Stage Theory of Carcinogenesis: A Critical Review Introducing the Concept of Modulation
Carcinogenesis is a long lasting process which, progressively, transforms part of a differentiated tissue to a malignant tumor. Initiation is the first event which introduces the tissue or some of its cells into that process. That event may be a physical (radiation) or a chemical mostly mutagenic treatment but also a viral infection or even a transfection of a piece of viral DNA (Lacey et al.1986). In most experimental protocols reported so far for viral and physical induction of cancer, only the initiation step seems to be required so that after a single or a few infections by the virus or a single or a few doses of irradiation is (are) sufficient to induce the appearance of malignant tumors in a majority of the animals. Eventhough such single step protocols do exist for the chemical induction of cancer using large doses of carcinogen, most of the protocols which are classically used for that purpose are multisteps in that sense that they involve a sequence of different treatments.
KeywordsMouse Skin Preneoplastic Lesion Carcinogenic Process Chemical Carcinogenesis Skin Carcinogenesis
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