Study
PLCO
(Learn more about this study)
Project ID
2010-0062
Initial CDAS Request Approval
Aug 5, 2010
Title
Natural History of Polyps Observed at Flexible Sigmoidoscopy
Summary
Colon polyps are regarded as precursors of colorectal cancer (CRC). However, the natural history of colon polyps is largely unknown. In a previous study, Stryker et al (1) performed a retrospective review of Mayo clinic records in the pre-colonoscopy era, using barium enema follow up of polyps = 10mm. Among 226 patients who were followed for 12 – 229 months, only 83 (37%) polyps enlarged. The cumulative risk of CRC (n = 21) was: 2.5% at 5 yrs, 8% at 10yrs, and 24% at 20 years. In another study, Hofstad et al (2) prospectively evaluated 116 patients in Norway. Per protocol, all polyps <10 mm found at colonoscopy were left in place for 3 years and annual colonoscopy was performed for redetection. The authors reported no net change in size of all polyps but noted that polyps <5 mm tended to grow, but polyps that were 5-9mm in size tended to regress, and the predictors of polyp growth were age (50-60yrs) and multiple (>4) polyps. The risk that patients may develop cancer if polyps, established cancer precursors, are left in the colon in order to study their natural history makes prospective evaluation unethical. In this proposal, we plan to study, albeit indirectly, the natural history of polyps among PLCO participants who had abnormal suspicious flexible sigmoidoscopy (FSG) screening at baseline T0, but did not undergo diagnostic colonoscopy. Rather, they had repeat FSG at years 3 or 5 of the trial (T3/T5). Many of these participants then had diagnostic colonoscopy to remove the polyps. This would give us an opportunity to study approximately 3000 PLCO participants in the largest study to assess the natural history of colon polyps to date, with an added advantage of prospective data collection.
Aims
Specific aim 1. To study the rate of growth of polyps in the distal colon over 3 to 5 years. We would like to assess the rate of growth of polyps seen with FSG, and analyse by polyp histology and size at baseline. We would also evaluate specific instance where a single polyp is seen at baseline, at repeat FSG 3-5 years later, and at diagnostic colonoscopy. We also plan to assess polyps growth rate when the same endoscopist perform FSG at baseline and at repeat FSG 3-5 years later. Specific aim 2. To study the comparative yield of colorectal adenoma and advanced pathological features by comparing patients who had diagnostic colonoscopy at baseline after abnormal suspicious FSG with those who had their polyps removed after 3-5 years of initial discorvery of colon polyps.
