The multistage model of cancer development: some implications.

The multistage model, introduced by Armitage and Doll, was very successful at describing many features of cancer development. Doll and Peto noted a significant departure below the prediction of the model and suggested that this could be due to undercounting of cases at older ages, or to the 'biology of extreme old age.' Moolgavkar pointed out that it could also be due to the approximation used.