Figure 1

Schematic diagram of colonic mucosa indicating progression of a field defect to colon cancer. The gray area within the right-hand set of irregular concentric areas indicates a colon cancer. The outermost irregular concentric areas indicate initial defects with a selective advantage. A next smaller concentric area indicates a secondary mutation or epimutation giving a further selective advantage, while still smaller areas indicated further mutations or epimutations with still further selective advantages.