A model with two stages and clonal expansion (TSCE) is reviewed as a protot
ype for biologically based models of cancer development. Applications of th
e TSCE model to data sets for animals and humans for particle radiation (a
particles) are presented. The results suggest that the radiation not only i
nfluences the initiating mutation, but may also act as a promoter. A possib
le mechanism for the promoting action is described. The consequences of the
se results for the shapes of the radiation dose-response curves at low dose
s and dose rates are discussed. (C) 2001 by Radiation Research Society.