Context The necessary frequency of endoscopic colorectal cancer screening after
a negative examination is uncertain.
Objective To examine the yield of adenomas and cancer in the distal colon found
by repeat flexible sigmoidoscopy (FSG) 3 years after a negative examination.
Design, Setting, and Participants Participants were drawn from the Prostate, Lung, Colorectal, and Ovarian
Cancer Screening Trial (PLCO), a randomized, controlled community-based study
of cancer screening. The mean (SD) age was 65.7 (4.0) years at study entry
(1993-1995) and 61.6% were men. Individuals underwent screening FSG at baseline
and at 3 years as part of the protocol and were referred to their personal
physicians for further evaluation of screen-detected abnormalities. Results
from subsequent diagnostic evaluations were tracked in a standardized fashion.
Of 11 583 eligible for repeat screening FSG 3 years after an initial
negative examination, 9317 (80.4%) returned.
Main Outcome Measures Polyp or mass detection in distal colon at year 3 repeat FSG; incidence
of adenoma or cancer in distal colon at year 3 examination; determination
of reason for detection (increased depth of insertion or improved preparation
at the year 3 examination or detection in a previously examined area).
Results A total of 1292 returning participants (13.9%) had a polyp or mass detected
by FSG 3 years after the initial examination. In the distal colon, 3.1% (292/9317)
were found to have an adenoma or cancer. The incidence of advanced adenoma
(n = 72) or cancer (n = 6) in the distal colon was 78 (0.8%) of 9317. Of individuals
with advanced distal adenomas detected at the year 3 examination, 80.6% (58/72)
had lesions found in a portion of the colon that had been adequately examined
at the initial sigmoidoscopy.
Conclusions Repeat FSG 3 years after a negative examination will detect advanced
adenomas and distal colon cancer. Although the overall percentage with detected
abnormalities is modest, these data raise concern about the impact of a prolonged
screening interval after a negative examination.