Advanced polyps increase CRC risk, but non-advanced polyps don’t

People whose colonoscopy revealed advanced adenoma may have a more than 2.5 times greater risk of colorectal cancer (CRC) than those with no adenoma, according to a recent study published in JAMA. But researchers also found that people with non-advanced adenoma had about the same risk for CRC as those with no adenoma.

“By demonstrating that individuals diagnosed with an advanced adenoma are at increased long-term risk for subsequent incident CRC, these findings support periodic, ongoing surveillance colonoscopy in these patients,” wrote researchers led by Robert E. Schoen, MD, MPH, professor of medicine and epidemiology, University of Pittsburgh School of Medicine, and chief of gastroenterology, hepatology, and nutrition, University of Pittsburgh Medical Center, Pittsburgh, PA.

In the United States, patients whose colonoscopy reveals one or two non-advanced adenomas—the most common pre-neoplastic finding—are advised to return in 5 to 10 years for another colonoscopy. But no evidence-based guidelines exist to advise clinicians on which patients should return in 5 years and which should return in 10.

“Bringing everyone back at 5 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,” Dr. Schoen said. “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.”

For this study, Dr. Schoen and colleagues included data from 15,935 participants (59.7% men, median age: 64 years) who underwent a colonoscopy as a result of their participation in the nationwide Prostate, Lung, Colorectal, and Ovarian (PLCO) cancer screening trial.

At baseline, researchers found:

• 18.1% of patients had an advanced polyp ( ≥ 1 cm, high-grade dysplasia, or tubulovillous or villous histology)
• 31.8% had a non-advanced polyp ( < 1 cm without advanced histology)
• 50.1% had no polyps

After a median follow-up of about 13 years, 196 patients developed CRC. The researchers found that those with advanced polyps were significantly more likely to develop CRC than those with no polyps (RR: 2.7, 95% CI: 1.9-3.7, P < 0.001). In addition, Dr. Schoen and colleagues found that in those with advanced polyps, cancer risk remained elevated throughout the following 15 years.

“After an advanced polyp has been removed, the whole colon remains at risk for cancer, and periodic colonoscopy is needed,” said Dr. Schoen.

However, there was no significant difference in CRC risk between patients with non-advanced polyps and those with no polyps (RR: 1.2, 95% CI: 0.8-1.7, P=0.30).

“That’s a provocative finding,” Dr. Schoen said. “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.”

This research was supported by the National Cancer Institute and the National Institutes of Health. Dr. Schoen received grant support from Medtronic.