Increased colorectal cancer risk after advanced adenoma detection

Last Updated: 2018-05-16

By Will Boggs MD

NEW YORK (Reuters Health) - The risk of developing colorectal cancer (CRC) is increased in individuals with an advanced adenoma at diagnostic colonoscopy prompted by CRC screening, according to findings from the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer trial.

Nonadvanced adenoma, however, did not appear to be associated with increased CRC risk, researchers report in the May 15 issue of JAMA.

"Patients with advanced adenomas should be encouraged to continue with follow-up surveillance," Dr. Robert E. Schoen of the University of Pittsburgh told Reuters Health by email. "They are a high-risk group, and we have every reason to think surveillance will be of benefit to them."

About a third of patients undergoing screening colonoscopy will have adenomatous polyps. Those with advanced adenomas are advised to return for follow-up colonoscopy in three years, and those with nonadvanced adenomas are advised to return in five to 10 years, with no clear evidence to determine who should return earlier as opposed to later.

Dr. Schoen and colleagues used data from nearly 16,000 participants in the PLCO study to examine the relationship between adenoma findings on diagnostic colonoscopy prompted by a positive screening result on flexible sigmoidoscopy and the long-term risk of CRC incidence.

At index colonoscopy, 18.1% of participants had advanced adenoma, 31.8% had nonadvanced adenoma and 50.1% had no adenoma.

During an overall median follow-up of 12.9 years, the incidence of CRC per 10,000 person-years was 20.0 in the advanced-adenoma group, 9.1 in the nonadvanced adenoma group, and 7.5 in the no-adenoma group.

The cumulative incidence of CRC over 15 years was significantly higher in the advanced-adenoma group (2.9%) than in either the nonadvanced-adenoma group (1.4%) or the no-adenoma group (1.2%). The incidence did not differ significantly in the latter two groups.

Within the advanced-adenoma group, the CRC incidence did not differ significantly between patients with adenomas of 1 cm or larger versus those with smaller adenomas but with advanced histology. Moreover, the CRC risk did not differ between years 5 to 10 compared with years 0 to 5.

Most detected CRCs were stage I or II (56.6%), 32.7% were stage III or IV and 10.7% were unknown.

Patients with advanced adenoma had significantly higher subsequent colonoscopy utilization and adenoma-removal rates, compared with patients with nonadvanced or no adenoma.

There were only 36 deaths overall from CRC, but participants with advanced adenoma were at significantly increased risk of CRC death compared with the two other groups, which had similar risks.

"I have been organizing for a randomized trial of 5- vs. 10-year surveillance for patients with 1-2 nonadvanced adenomas," Dr. Schoen said. "I think this is an important next step, and these results point to the uncertainty over what we are currently doing and why embarking on such an experiment is reasonable and worthwhile. We are consuming a lot of resources for uncertain benefit."

Dr. Joseph C. Anderson from Veterans Affairs Medical Center, in White River Junction, and The Geisel School of Medicine at Dartmouth, in Hanover, New Hampshire, recently examined factors associated with shorter colonoscopy surveillance intervals for patients with low-risk colorectal adenomas. He told Reuters Health by email, "I think that these data support previous published studies as well as those recently presented at meetings. Specifically, 1-2 low-risk adenomas are not associated with an increased long-term CRC risk."

"A major question is, what is the risk for 3 or more adenomas?" he said. "This group has long been considered a high-risk group based on previous studies, such as the National Polyp Study, that showed that the risk for metachronous advanced adenomas was significantly increased. The current data seem to suggest the opposite based on CRC, which is a better outcome (to use) than advanced adenomas."

"Certainly, these data support the current guideline recommendations for 1-2 low-risk adenomas, which is 5 to 10 years," said Dr. Anderson, who was not involved in the new study. "Perhaps 10-year intervals should be recommended for low-risk adenomas."

SOURCE: https://bit.ly/2rJqN8D

JAMA 2018.