Identification of the cell regulatory genes that drive carcinogenesis is one of the major goals in cancer research, resulting in new anticancer drug targets and new therapeutic and diagnostic approaches. Colon cancer is one of the best-characterized tumor systems from the perspective of understanding the genetic events that underlie the development of malignancy. One reason for the detailed knowledge available in this system is the identification of an intermediate in the progression pathway, the adenomatous polyp, accessible for both histological and molecular analysis. Characterization of the polyp intermediate has allowed discrimination between initiating events and progression events. Mutations in the APC gene, for example, are found in the earliest polyps, initiating the development of both inherited and sporadic colon adenomas (