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MULTISTAGE PROGRESSION                                       39


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                              Figure 3.1  Morphology of normal colon tissue. Labels show surface epithelium
                              (SE), colon crypts (CC), goblet cells (GC), lamina propria (LP), and muscularis
                              mucosa (MM). The crypts open to the surface epithelium—in this cross section,
                              some of the crypts appear partially or below the surface. From Kinzler and
                              Vogelstein (2002), original published in Clara et al. (1974).




                                     3.3 Multistage Progression in Colorectal Cancer

                                Colorectal cancer provides a good model for the study of morpholog-
                              ical and genetic stages in cancer progression (Kinzler and Vogelstein
                              2002). Various precancerous morphologies can be identified, allow-
                              ing tissue samples to be collected and analyzed genetically. Figure 3.1
                              shows the morphology of normal colon tissue. The epithelium has about
                                7
                              10 invaginations, called crypts. Cells migrate upward to the epithelial
                              surface from the dividing stem cells and multiplying daughter cells at
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