Outline the stages of carcinogenesis.
Cancer biologists have realised now that the i processes of carcinogenesis is very complex, involving many events but to simplify the process it can be divided into at least three stages initiation, promotion and progression.
1) Initiation - The fist stage initiation results from an irreversible genetic alteration, most likely one or more mutations. It is difficult to identify and isolate initiated cells, except in some experimental conditions. One such example is the initiation of liver cancer in
rats by a known chemical carcinogen aflatoxin. Most initiated cells never proceed to the next stage of cancer formation and scientists fear that adult organism contain many initiated cells in most organs.Therefore. the first step of cancer is a very common event that often occurs spontaneously and may be induced readily in animals and humans.
2) Promotion - The second stage or promotion is reversible and does not involve changes in structure of DNA but rather in the expression of the genome of the initiated cell. This results from an interaction
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