Chimeric nonhuman mammals useful as inducible spontaneous cancer models are disclosed. The nonhuman mammals are obtained by introducing one or more genetically modified embryonic stem (ES) cells into an early stage embryo, and then implanting the manipulated embryo into a surrogate mother. The ES cells contain a recombinant oncogene, and also may contain a genetic mutation that deletes or inactivates a tumor suppressor gene. Models of different types of cancer are produced by introducing different combinations of genetic mutations into the ES cells that are introduced into the early stage embryo.