Background: Despite regular colonoscopy, interval colorectal cancer (CRC) may occur. Long-term studies examining CRC rates in patients with previous colonoscopy are lacking.
Objective: We examined the rate of interval CRC in the Polyp Prevention Trial Continued Follow-up Study (PPT-CFS), an observational study of PPT participants that began after the PPT ended.
Setting: A national U.S. community-based polyp prevention trial.
Main outcome measurements: Medical records of patients with CRC were collected, reviewed, and abstracted in a standardized fashion.
Results: Among 2079 PPT participants, 1297 (62.4%) agreed to participate in the PPT-CFS. They were followed for a median of 6.2 years after 4.3 years of median follow-up in the main PPT. Nine cases of CRC were diagnosed over 7626 person-years of observation (PYO), for an incidence rate of 1.2/1000 PYO. The ratio of CRCs observed compared with that expected by Surveillance, Epidemiology, and End Results was 0.64 (95% CI, 0.28-1.06). Including all CRCs (N = 22) since the beginning of the PPT, the observed compared with expected rate by Surveillance, Epidemiology, and End Results was 0.74 (95% CI, 0.47-1.05). Of patients in whom CRC developed in the PPT-CFS, 78% had a history of an advanced adenoma compared with only 43% of patients who remained cancer free (P = .04).
Limitation: A relatively small number of interval cancers were detected.
Conclusions: Despite frequent colonoscopy during the PPT, in the years after the trial, there was a persistent ongoing risk of cancer. Subjects with a history of advanced adenoma are at increased risk of subsequent cancer and should be followed closely with continued surveillance.
2010 American Society for Gastrointestinal Endoscopy. Published by Mosby, Inc. All rights reserved.