The model of carcinogenesis in which the basic idea is that the essential variable determining the change in the risk is not age, but time period. The model proposes that the cancer of a particular tissue that develops according to the process stated below:
* A normal cell develops into the cancer cell by the small number of transitions through the series of intermediate steps;
* In beginning, the number of normal cells at risk is very large, and for each of the cell a transition is quite rare event;
* The transitions are independent and free of one another #question..