Economic Models of Colorectal Cancer Screening in Average-Risk Adults Workshop Summary (2005) / Chapter Skim
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Appendix P Natural History of Colorectal Adenomas and Cancer--T. R. Levin, M.D.
Appendix P Natural History of Colorectal Adenomas and Cancer--T. R. Levin, M.D.
Pages 263-284
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Appendix P Natural History of Colorectal Adenomas and Cancer T
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264 ECONOMIC MODELS OF COLORECTAL CANCER SCREENING SLIDE 2 SLIDE 2 NOTES: No notes.
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. Can that study be interpreted to suggest that 40 percent of distal cancers arise de novo?
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The others were all beyond the reach of sigmoidoscopy and might be classified as left-sided cancers. When these findings are compared with the Kaiser sigmoidoscopy findings (previous slide)
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This result is not much different from the findings of the National Polyp Study.
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That rate is somewhat lower than was reported in the PLCO trial, probably because the individuals in this study developed diagnosed cancer, whereas in PLCO some cancers were found through rescreening.
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. Would that imply that roughly 15 percent of the cancers are de novo?
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One is the 80 percent reduction in colorectal cancer incidence over the follow-up period. Does that mean that we cannot prevent 20 percent of cancers because they are effectively de novo at present?
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They may be more common in women, especially as we are learning that proximal cancers appear to be more common in women and de novo cancers are more likely to be proximal cancers. African Americans may also have a higher rate of de novo cancers than do Caucasians.
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. Those very few studies found that it took about 10 to 15 years before cancer developed.In a study of cancers in patients with polyps removed, Atkin found an average 14 year lapse (Atkin et al., 1992)
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. That Mayo Clinic report suggests that about 75 percent of large polyps found on barium enema and left unresected for various reasons never progressed to cancer in the 20-year period of observation .
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Probably the three largest studies that have looked at this in living patients (with endoscopy) have been the VA Cooperative Study, the Lilly Colonoscopy Study by Tom Imperiale, and our study at Kaiser (Levin et al., 1999; Imperiale et al., 2000; Lieberman et al., 2000)
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. Our study was prospective, so we were not dependent on retrospective review of electronic and paper medical records, as some studies were.
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Indeed, age alone is a stronger predictor than the presence of a distal tubular adenoma. Distal adenoma size did not enter into the CART analysis at any level.
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. The two studies indicate that about 60-70 percent of clinically important lesions in the proximal colon can be found through following patients with lesions in the distal colon.
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That implies that colonoscopy provides an incremental benefit over sigmoidoscopy to only 3 or so percent of the screened population (Lewis et al., 2003)
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(The relatively young age of the people in that study, however, may have an effect on these findings.) The dietary intervention studies, which involve periodic surveillance with colonoscopy, also show that individuals with one or two small adenomas rarely get subsequent cancers.
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That analysis is based on a comparison of autopsy data and clinical reports of prevalence of cancers at different stages (Koretz, 1993)
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I would propose that the method of detection of cancers and polyps may also interact with the genotype or phenotype or prognosis. It may be that cancers detected with stool marker tests that search for a certain molecular panel of fecal DNA may be different in their molecular distribution from those detected by more traditional fecal occult blood tests.
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Those that do will take a long time. Some cancers will arise de novo, but we cannot know at present whether they are inherently unique biologically or whether they grew from adenomas that were missed on colonoscopy.
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2003. A case-cohort study for the disease natural history of adenoma-carcinoma and de novo carcinoma and surveillance of colon and rectum after polypectomy: implication for efficacy of colonoscopy.
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2003. Male gender adversely affects survival following surgery for colorectal cancer.
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