DISEASE CHARACTERISTICS: Histologically documented colorectal cancer that has been curatively resected, including: Dukes' A/B1 (T1-2, N0, M0) Dukes' B2/C (T3, N0, M0 and any T, N1, M0) disease-free more than 5 years post-resection Colonoscopy to the cecum (or small bowel anastomosis) with removal of all polyps required within 4 months of entry Preparation must be adequate to visualize mucosa and discern the presence of no further polyps No familial polyposis (more than 100 polyps at time of resection) No history of inflammatory bowel disease including ulcerative colitis or Crohn's disease