The genetic construction of cancer-prone mice, combined with the capacity to control transgene expression in vivo, provides new opportunities to study the role of oncogenes in the maintenance of fully formed tumors. These inducible cancer models provide a means to dissect how specific oncogenic signals influence host-tumor symbiosis, to validate the importance of a given oncogenic lesion in established advanced tumors, and to predict the biological response and adaptations to therapies targeted to that cancer-causing genetic alteration.