Background: The appropriate interval for rescreening after a negative colonoscopic examination remains uncertain. Recommendations to perform colonoscopy every 10 years are based on case-control studies that suggest sigmoidoscopy screening reduces mortality from distal colorectal cancer for up to 10 years. Direct data to assess the validity of this recommendation is lacking. To determine an appropriate follow-up interval, Imperiale and colleagues identified persons with no adenomas on baseline screening colonoscopy who were rescreened after five years.

The Study: The authors retrospectively reviewed 2,436 patients from the Lilly Colorectal Cancer Prevention Program. Patients were eligible for inclusion if they had a baseline colonoscopy with no adenomatous polyps identified, and a rescreening colonoscopy after five years. Patients were at least 50 years of age and were asymptomatic at their initial examination.

Results: A total of 1,256 (51.6 percent) of patients were rescreened after five years. Colonoscopy to the cecum was documented in 94 percent of patients at baseline and 97 percent of patients at the follow-up examination. No serious complications were reported at either examination.

No colon cancers were found on rescreening, although 16 percent of patients had at least one adenoma. Sixteen of the 1,256 patients (1.3 percent) had at least one advanced adenoma, which was defined as a tubular adenoma 1 cm or larger in diameter, a polyp with a villous component of at least 25 percent, or a polyp with high-grade dysplasia. Of the 19 advanced adenomas, 10 were found distal to the splenic flexure. The authors calculated that 79 patients would need to be rescreened after five years to detect one advanced adenoma, although there was a difference between sexes (55 for men and 182 for women).

Adenomas were more frequently found on rescreening in patients with hyperplastic polyps on baseline colonoscopy than in patients who had no polyps on baseline colonoscopy (23.6 versus 14.6 percent, relative risk = 1.62). However, there was no statistical association of hyperplastic polyps and advanced adenomas.

Conclusion: The five-year risk of colorectal cancer is low among patients who had a normal baseline screening colonoscopy. The authors support a rescreening interval of five years or longer after a normal colonoscopic examination.

editor's note: Although using a 10-year rescreening interval instead of a five-year interval would have helped examine the validity of current guidelines, this study does demonstrate a low risk of colon cancer for at least five years after a normal colonoscopy. Perhaps a more pressing question is whether physicians are doing enough to screen for colon cancer in the first place. As of 2006, the Centers for Disease Control and Prevention reported that only two states (Connecticut and Rhode Island) achieved screening rates above 70 percent, according to existing guidelines.¹ Most states achieved a screening rate of less than 60 percent.¹ Recommendations published in 2008 reaffirm the acceptability of several options for colorectal cancer screening (see accompanying table).^2,3 Routinely offering a choice from these options may increase screening rates, especially in patients who may be reluctant or unable to tolerate colonoscopy.—k.t.m.

ACR = American College of Radiology; ACS = American Cancer Society; CT = computed tomography; DCBE = double contrast barium enema; FOBT = fecal occult blood testing; USMSTFCC = U.S. Multi-Society Task Force on Colorectal Cancer; USPSTF = U.S. Preventive Services Task Force.

*— The USPSTF recommends routine colorectal screening for adults 50 to 75 years of age. Adults 76 to 85 years of age should not be screened routinely, but there may be considerations that support screening in individual patients. Adults older than 85 years should not be screened.

†— Beginning at 50 years of age.

Information from references ² and ³ .