The authors developed a mouse cancer model to evaluate oncogene cooperativity in the development of tumours. Stochastic gene expression was induced using a 'Multi-Hit' transgene containing three oncogenes that can be independently activated by the Cre recombinase to mimic the stepwise development of specific cancers. The authors suggest that future experiments using this model may show whether pathway interactions are affected by tumour suppressor functions, and they suggest that the model could be useful in predicting the effectiveness of drug treatments.