The utilization of mice as a model for human cancer goes back to the generation of inbred laboratory strains in the early twentieth century. Some inbred mouse strains were genetically predisposed to certain types of cancer, providing an early indication that genetic manipulation of a species could provide novel insights into the processes of tumorigenesis (1 ,2 ). The development of transgenic and knockout technologies has extended our ability to manipulate the mouse genome and has greatly facilitated modeling of the genetic and biologic aspects of cancer (3 –6 ).