title: Reversible and irreversible lesions in processes of cancer development.
abstract: Most known carcinogenic processes consist of a multistep sequence in which new cell populations are the links in the chain of events triggered by the chemical carcinogen. Although the later steps are self-generating, in that they require no obvious external stimulus, the early steps are very much environment-dependent. Initiation of chemical carcinogenesis appears to consist of at least two steps, a reversible biochemical one and a round of cell proliferation which results in the generation of a relatively permanent, irreversible rare event, the promotion of initiated cells. The selection of these cells - promotion - is largely reversible, with only an occasional selected focal area of proliferation persisting to the next step, again a rare event. The selections of this and subsequent rare events are largely unknown as to their reversibility. The need to delineate each step is emphasized.
mesh_terms: D000818:Animals; D002273:Carcinogens / Q000378:metabolism*; D002471:Cell Transformation, Neoplastic; D005260:Female; D006801:Humans; D008099:Liver / Q000378:metabolism; D008297:Male; D008321:Mammary Glands, Animal / Q000378:metabolism; D051379:Mice; D009369:Neoplasms / Q000209:etiology*; D051381:Rats; D012867:Skin / Q000378:metabolism; D013997:Time Factors
chemical_list: D002273:Carcinogens