SAN DIEGOA longer surveillance interval of 6 years or more may
be appropriate for low-risk postpolypectomy patients, said Ann G.
Zauber, PhD, of the Department of Epidemiology and Biostatistics,
Memorial Sloan-Kettering Cancer Center. Dr. Zauber presented the
study findings at the American Gastroenterology Association (AGA)
meeting held during the Digestive Disease Week conference.
She collaborated with Dr. Sidney Winawer of Memorial Sloan-Kettering
on the project.
Dr. Zauber cited an earlier National Polyp Study (NPS) report of
1,418 adenoma patients, which showed that colonoscopic polypectomy
with surveillance reduced colorectal cancer incidence by 76% to 90%.
Dr. Zauber noted that the malignancies were far less than
expected. We wanted to understand if the incidence reduction was due
to the initial polypectomy or to surveillance, she said.
Dr. Zauber explained that the relative effect of the initial
polypecto-my vs surveillance colonoscopy on incidence reduction has
implications for follow-up intervals, screening colon-oscopy studies,
and understanding the adenoma-carcinoma progression.
The researchers used a Micro-Simulation Screening Analysis (MISCAN)
model (developed at Erasmus University, Rotterdam, in conjunction
with the National Cancer Institute) and NPS data to predict
colorectal cancer incidence in three groups: patients with no initial
polypectomy or surveillance, patients with polypectomy only, and
patients with both an initial polypectomy and sur-veillance.
The model demonstrated a dramatic reduction in the expected incidence
of colorectal cancer with an initial polypectomy with or without
surveillance, leading the researchers to conclude that it is the
initial polypectomy that accounts in large part for the reduction in
colorectal cancer incidence. The model did, however, predict a modest
benefit from surveillance after 6 years.
Colonoscopy is very effective for detecting significant
adenomas, Dr. Zauber said. There wasnt much impact
with the follow-up surveillance.
She said that the research team will undertake a longer term study
later this summer analyzing a 6-year surveillance interval for
low-risk patients and a 3-year interval for higher risk patients.