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
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
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