May 15, 2018
2 min read

Colon cancer risk depends on polyp type found during colonoscopy

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Robert E. Schoen
Robert E. Schoen

The risk for colorectal cancer is about 2.5 times higher in patients who have advanced adenomatous polyps detected during colonoscopy vs. those with no adenomas, but the risk does not appear to be increased among patients with non-advanced adenomas, according to new research published in JAMA.

These findings suggest that repeat colonoscopy may not be required as frequently for patients with non-advanced adenomas, according to Robert E. Schoen, MD, MPH, professor of medicine and epidemiology at University of Pittsburgh School of Medicine, and chief of the division of gastroenterology, hepatology and nutrition at University of Pittsburgh Medical Center, and colleagues.

With screening colonoscopy, “one can actually prevent people from getting cancer, which is far better than just detecting it early,” Schoen said in a press release. “But polyps are commonly found, and patients can find themselves returning for frequent follow-up colonoscopy procedures.”

To evaluate the long-term risk for colorectal cancer based on adenoma findings during screening colonoscopy, Schoen and colleagues performed a prospective cohort study of 154,900 participants in a randomized controlled trial, 15,935 of whom underwent colonoscopy after a positive flexible sigmoidoscopy (59.7% men; 90.7% white; median age, 64 years). Enrollment began in 1993 and researchers followed participants through 2013 at multiple U.S. sites (median follow-up, 12.9 years).

Colonoscopy detected an advanced adenoma in 2,882 (18.1%) of the participants, a non-advanced adenoma in 5,068 (31.8%) and no adenoma in 7,985 (50.1%).

Among those with an advanced adenoma, 70 developed colorectal cancer (incidence rate, 20 per 10,000 person-years [95% CI; 15.3-24.7]). Among those with a non-advanced adenoma, 55 developed CRC (incidence rate, 9.1 [95% CI, 6.7-11.5]) and among those with no adenoma, 71 developed CRC (incidence rate, 7.5 [95% CI, 5.8-9.7]).

Thus, advanced adenomas were significantly associated with an increased risk for CRC vs. no adenoma (RR = 2.7; 95% CI, 1.9-3.7; P < .001), while non-advanced adenomas were not (RR = 1.2; 95% CI, 0.8-1.7; P = .30). Additionally, advanced adenomas were associated with a significantly increased risk for CRC mortality vs. no adenomas (RR = 2.6; 95% CI, 1.2-5.7; P = .01), while again non-advanced adenomas were not (RR = 1.2; 95% CI, 0.5-2.7; P = .68).

“After an advanced polyp has been removed, the whole colon remains at risk for cancer, and periodic colonoscopy is needed,” Schoen said in the press release. That patients with non-advanced adenomas carried a similar CRC risk to those with no adenomas is “a provocative finding,” he added. “It would suggest that if you have a polyp that is non-advanced, which is the case in about one-third of people undergoing screening, you don’t need to come back as frequently for colonoscopy because your risk of cancer is the same as if you didn’t have any polyps.”

Practice guidelines in the U.S. currently recommend that individuals with one or two non-advanced adenomas return for screening in 5 to 10 years, but evidence is lacking on which patients should return at 5 vs. 10 years, Schoen and colleagues wrote.

“Bringing everyone back at five years is incurring a lot of testing that may not be preventing much cancer because only a small fraction of polyps will ever turn into cancer,” he said in the press release. “Millions of people are receiving follow-up colonoscopy exams for non-advanced polyps. We need to find out what is necessary. Potentially, this is an area where we could reduce testing and costs.” – by Adam Leitenberger

Disclosures: The authors report no relevant financial disclosures.