Stochastic modelling of colon cancer: is there a role for genomic instability?

Three stochastic models of genomic instability recently developed by Little and Wright (Math. Biosci., (2003) 183, 111–34), with two, three and five stages, and the two-stage genomic instability model of Nowak et al. (Proc. Natl Acad. Sci. USA, (2002) 99, 16226–16231) are compared with the four-stage model proposed by Luebeck and Moolgavkar (Proc. Natl Acad. Sci. USA, (2002) 99, 15095–15100) that does not assume such an instability mechanism. All models are fitted to US colon cancer incidence data. The best fitting models are the two-stage model of Nowak et al. and the two-stage model of Little and Wright, with the four-stage model of Luebeck and Moolgavkar not markedly inferior. The fits of the three-stage and five-stage models are somewhat worse (P <0.05), the five-stage model fitting particularly poorly (P <0.01). Both optimal genomic instability models predict cellular mutation rates that are at least 10 000 times higher after genomic destabilization, for both sexes. Therefore, the results of this paper are somewhat at variance with those of previous analyses of Little and Wright in suggesting that equivalently good fit may be obtained by models that do not assume a role for genomic destabilization in the induction of colon cancer as for those that do.