Birth and death/differentiation rates of papillomas in mouse skin

A simple one-stage model for the formation of papillomas is used to evaluate data from a series of initiation/promotion/stop-promotion experiments performed on NMRI mice. These experiments used a single application of 100 nmol 7,12-dimethylbenz[a]anthracene followed by twice weekly applications of 5 nmol 12-O-tetradecanoylphorbol-13-acetate. It is shown that, on the basis of this model, the data considered here provide no evidence for a growth advantage of initiated cells versus normal cells. Although model estimates always have to be treated with utmost caution, they can at least be interpreted in a qualitative way. In consequence, it has to be concluded either that the mechanism upon which the model is based fails to describe properly the growth behaviour of initiated cells, or that initiated cells do not possess a growth advantage over normal cells, even in the presence of a promoter.