NEW ORLEANS--Colorectal cancer surveillance intervals can be lengthened for some patients following initial polypectomy, two large studies suggest.
Six-year follow-up data from the National Polyp Study showed that newly diagnosed patients with three or more adenomas at initial colonoscopy were at high risk for future polyps and should be re-examined at three years. But surveillance for patients with a single adenoma at baseline could be extended to at least six years, Ann G. Zauber, PhD, of Memorial Sloan-Kettering Cancer Center, reported at the American Society of Preventive Oncology annual meeting.
Current surveillance colonoscopy recommendations are not cost-effective, several speakers said at the meeting. It takes 320 colonoscopies to identify one colo-rectal cancer. But 3% of adenomas found at 3-year follow-up colonoscopy are advanced and 0.6% are invasive cancer.
"This suggests that routine follow-up as currently recommended occurs too late for some patients but too early for most patients. The surveillance interval should be individualized, if possible," said Wei Zheng, MD, PhD, of the University of Minnesota, Minneapolis.
Dr. Zheng was the principal investigator for a large study of 1,490 adenoma patients in Zheijiang, China, which found that risk of metachronous adenomas, especially advanced neoplasms, is closely related to the pathologic characteristics of the initial adenomas.
National Polyp Study Results
In the National Polyp Study mentioned above, 337 patients underwent two or three surveillance colonoscopies by the end of six years. Researchers were looking for baseline characteristics that might predict risk for future disease.
At follow-up, 8% of patients had adenomas with advanced pathology (larger than 1 cm, high-grade dysplasia, or infiltrating cancer); 42% had other adenomas (1 cm or smaller, no high-grade dysplasia, no infiltration); and 49% had no adenomas detected.
The greatest predictor of risk was number of adenomas at baseline: three or more polyps carried an odds ratio of 15.7 for adenomas with advanced pathology. Fifteen (20%) of 74 patients with three or more adenomas at baseline had advanced adenomas, compared with 7 (4%) of 187 patients with a single baseline adenoma.
Patients with a family history of colo-rectal cancer and who were age 60 years or older at initial diagnosis were at an increased risk of 7.3, Dr. Zauber said.
Of the 28 patients with advanced adenomas at follow-up, 20 fell into the high-risk category, either because of having multiple adenomas present initially or being age 60 or older with a family history. Five of these adenomas were malignant, and the others were large adenomas not yet cancerous.
"This constitutes a relatively good baseline classification for patients who need exams every three years," Dr. Zauber said. "On the other hand, patients with one or two adenomas at baseline, no parental history of colorectal cancer, or initial diagnosis under age 60 can go six or more years before surveillance."
In the Chinese cohort, 280 of the 1,490 patients aged 30 and older developed adenomas in the distal colon and rectum in the 16-year follow-up period. Patients with large adenomas with severe dysplasia were found to have a very high risk (a 37-fold increase) of advanced recurrent adenomas in the future. These patients need close surveillance, Dr. Zheng said.
A 14-fold relative risk of advanced recurrent adenomas was found for patients whose initial adenomas contained a high degree of dysplasia. Villous/tubulovillous adenomas (as opposed to tubular) carried an 8.0 relative risk, and patients with baseline adenomas larger than 1.0 cm had a relative risk of 4.3