Abstract: 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.

Abstract: The invention provides an improved directed complementation method for generating a conditionally tumorigenic mouse cell. In a directed complementation method, the tumorigenicity of a conditionally tumorigenic mouse cell depends on either the expression of an inducible recombinant oncogene or the expression of a recombinant gene of interest that functionally complements an uninduced recombinant oncogene. The invention provides a method of producing a tumorigenic mouse cell containing an uninduced oncogene, a recombinant gene of interest that functionally complements the uninduced oncogene, and a Cre-ER system capable of excising the recombinant gene of interest. When the Cre-ER system is activated, the recombinant gene of interest is excised. From the effect on the mouse cell it is possible to determine whether the recombinant gene of interest is a tumor maintenance gene.