People who are found to have advanced polyps during a colonoscopy have a long-term risk of colorectal cancer that is more than 2.5 times greater than for those without polyps. In contrast, those with non-advanced polyps have a colorectal cancer risk that is similar to people in whom no polyps are found. Those findings, which raise important questions about how often one needs to return for repeat colonoscopies after polyps are identified, arise from a long-term study conducted by researchers at the University of Pittsburgh School of Medicine and UPMC and published today in the JAMA.

Colorectal cancer screening is effective because identifying polyps and removing them prevents cancers from developing. “One can actually prevent people from getting cancer, which is far better than just detecting it early,” said senior author Robert E. Schoen, MD, MPH, professor of medicine and epidemiology at Pitt’s School of Medicine, and chief of the division of gastroenterology, hepatology, and nutrition at UPMC. “But polyps are commonly found, and patients can find themselves returning for frequent follow-up colonoscopy procedures.”

To determine the risk of developing colorectal cancer after finding polyps, the study looked at data from 15,900 participants nationally who underwent a colonoscopy as a result of their participation in the Prostate, Lung, Colorectal, and Ovarian Cancer screening trial. Patients were followed for up to 15 years. At baseline, the researchers found that 18% of patients had an advanced polyp; 32% had a non-advanced polyp, and 50% had no pre-cancerous polyps.

For people with advanced polyps, the study showed that cancer risk is not just in the first years after the polyp was removed, but the risk remained elevated throughout the ensuing 15 years.

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

Intriguingly, the study also showed that people with non-advanced polyps had a risk for cancer similar to a person without polyps.

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

Current guidelines in the United States recommend that people with one or two non-advanced polyps return for screening in 5 to 10 years. However, there is no guidance about who should return in which time period.

“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,” said Schoen. “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.”

Studies to evaluate the benefit of repeat colonoscopy at 5 years for people with non-advanced polyps are currently being considered. The authors note that efforts to ensure that people with advanced adenomatous polyps come back and are compliant with follow-up testing may be important to prevent colon cancer.