Schoen RE, Pinsky PF, Weissfeld JL, Bresalier RS, Church T, Prorok P, Gohagan JK, for the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial
Group . Results of Repeat Sigmoidoscopy 3 Years After a Negative Examination. JAMA. 2003;290(1):41-48. doi:JOC30147
Author Affiliations: Departments of Medicine and Epidemiology and the University of Pittsburgh Cancer Institute, University of Pittsburgh, Pittsburgh, Pa (Drs Schoen and Weissfeld); Division of Cancer Prevention, National Cancer Institute, Bethesda, Md (Drs Pinsky, Prorok, and Gohagan); Division of Gastrointestinal Medicine and Nutrition, M. D. Anderson Cancer Center, Houston, Tex (Dr Bresalier); and Division of Environmental and Occupational Health, University of Minnesota, Minneapolis (Dr Church).
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.
Limited evidence supports a recommended frequency of endoscopic colorectal
cancer screening after a negative examination. One option recommended by consensus
guidelines is a screening colonoscopy every 10 years.1 The
data supporting this interval stem largely from a case-control study of sigmoidoscopy2 that found a higher rate of sigmoidoscopy in controls
compared with distal colorectal cancer cases. In that study, the negative
association of sigmoidoscopy with mortality due to cancer persisted for up
to 10 years. In contrast, a Veteran's Administration case-control study of
endoscopy use demonstrated an effect of endoscopy for only up to 6 years.3,4
The recommended interval for repeat screening flexible sigmoidoscopy
(FSG) after a negative examination is 5 years.1,5 A
number of small case series demonstrate widely varying rates of abnormal findings
on follow-up after a negative examination, up to 7% for detection of adenomas
and 1% to 2% for detection of advanced adenomas after as little as 1 year.6- 11 Only
a few small colonoscopy studies have reported the results of repeat examination
after a negative examination, and all comprise selected patient populations.12- 14
Determining the incidence of adenoma after a negative examination is
complicated by the inherent limitations in endoscopic detection of prevalent
adenomas. Several studies using tandem colonoscopy, or colonoscopy by one
practitioner followed immediately by another colonoscopy by a second, have
shown that adenomas, especially small adenomas, are easily missed. Miss rates
have ranged from 13% for adenomas smaller than 1 cm15 to
27% for adenomas smaller than 5 mm.16 In 1
tandem study, 6% of adenomas sized at least 1 cm were missed.16 Whether
lesions are missed or represent new growth, an understanding of the expected
yield from subsequent examinations is critical to establishing informed guidelines
for follow-up. To our knowledge, no study has reported large-scale results
of repeat screening after a negative examination.
The Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO)
is a randomized, controlled community-based study evaluating the effectiveness
of cancer screening tests on site-specific cancer mortality. Sponsored by
the National Cancer Institute, the trial is being conducted in 10 screening
centers in the United States.17 For the colorectal
cancer end point, the trial is evaluating the effect of 60-cm FSG on colorectal
cancer mortality. In the initial trial design, sigmoidoscopy was performed
in the intervention group at inception and again at 3 years. In keeping with
prevailing practice, the interval between examinations was subsequently extended
to 5 years. In this investigation, we examine the yield of a repeat FSG examination
3 years after an initial negative examination.
Participants in this study were taken from the intervention arm of the
PLCO trial. Randomization began in November 1993 and was completed in July
2001, with more than 154 000 people aged 55 to 74 years enrolled. Those
randomized before December 1995 received FSG at enrollment and 3 years later.
The 10 PLCO centers are located in the following cities: Washington, DC; Detroit,
Mich; Salt Lake City, Utah; Denver, Colo; Honolulu, Hawaii; Minneapolis, Minn;
Marshfield, Wis; Pittsburgh, Pa; St Louis, Mo; and Birmingham, Ala. Participants
in the intervention arm undergo periodic cancer screening tests, including
chest radiograph, FSG, digital rectal examination and prostate-specific antigen
screening (for men), and cancer antigen 125 screening and vaginal ultrasound
(for women). A baseline questionnaire recorded personal sociodemographic characteristics,
medical history, cancer screening history within the previous 3 years, and
family history. Participants were recruited into the PLCO trial through mass
mailings and met the following eligibility criteria: (1) age 55 to 74 years;
(2) no current treatment for cancer except basal cell or squamous cell skin
cancer; (3) no known prior cancer of the colon, rectum, prostate, lung, or
ovaries; (4) no surgical removal of the colon, lung, ovary, or prostate; (5)
no participation in another cancer screening or cancer prevention trial; (6)
no finasteride use (in men) or no tamoxifen use (in women) in the past 6 months;
(7) provision of informed consent; (8) no more than 1 prostate-specific antigen
test in the past 3 years (for men randomized after April 1995); and (9) no
colonoscopy, sigmoidoscopy, or barium enema in the past 3 years (for individuals
randomized after April 1995).
Flexible sigmoidoscopy examinations were performed by trained nurses
or certified physicians. Examiners used depth of insertion, adequacy of bowel
preparation, and primary visual findings to place each sigmoidoscopy examination
into 1 of 4 mutually exclusive hierarchical result categories. The abnormal suspicious result category signified any finding of polyp
or mass, regardless of size or technical adequacy of the examination. The inadequate result category signified less than a 50-cm
depth of insertion or estimated visualization by the examiner of less than
90% of the mucosal surface due to inadequate bowel preparation. The abnormal not suspicious result category signified any abnormality
other than a mass or polyp (eg, hemorrhoids or diverticulosis) in a technically
adequate examination. Finally, the negative result
category signified a technically adequate examination without a polyp, mass,
or incidental abnormality.
An FSG examination was considered positive if the examiner noted a polypoid
lesion or mass. At sigmoidoscopy, the examiner recorded the location and shape
and estimated the size of each of the 4 largest lesions. Lesions were usually
not biopsied or removed. Individuals were referred to their personal physicians
for evaluation of screening-detected abnormalities and were tracked to determine
the results from subsequent diagnostic workup. Data on diagnostic follow-up
with repeat FSG or colonoscopy were collected using trained medical record
abstractors, who recorded the pathologic findings, size, and location of each
lesion found. The anatomical site of lesions was recorded as rectum, sigmoid
colon, descending colon, splenic flexure, transverse colon, hepatic flexure,
ascending colon, or cecum, and, when available, the distance in centimeters
to the lesion was documented.
For classification of abnormalities found on subsequent colonoscopy,
a lesion in the rectum, sigmoid colon, or descending colon was considered
distal. If the anatomical site was not recorded and the distance was, then
a lesion at a distance of less than 50 cm into the colon was considered distal.
Any lesion with a recorded anatomical location from the splenic flexure to
the cecum or a lesion with no recorded location but a distance of at least
50 cm into the colon was considered proximal. Pathologic results were obtained
from the local community pathologist report. An adenoma was defined as advanced
if it contained villous features (villous or tubulovillous adenomas), was
large (≥1 cm as estimated by the endoscopist), or had severe dysplasia.
Carcinoma in situ was classified as severe dysplasia.
Individuals included in the current study were randomized to the screening
intervention, had an initial FSG that showed no polypoid abnormality or mass,
and, by protocol, underwent repeat screening FSG 3 years after the initial
examination. Individuals with other abnormalities at initial FSG (eg, diverticulosis
or hemorrhoids) are included, as are individuals with inadequate examinations
due to inadequate preparation or depth of insertion of less than 50 cm.
To determine whether a lesion detected as a result of repeat sigmoidoscopy
was due to increased depth of insertion or improved preparation at the second
examination, the depth of insertion at the initial examination, the depth
of insertion at the year 3 examination, and the size and location of the abnormal
finding at the year 3 examination were recorded and compared.
Lesions were classified as detected possibly because of increased depth
of insertion or improved preparation at the year 3 examination or detected
in a previously examined area. All lesions found at the year 3 examination
in participants with an inadequate examination at baseline due to poor preparation
were considered detected because of improved preparation. When the depth of
insertion was greater in year 3 than at baseline, the anatomical location
of the lesion was reviewed. The colon was classified into the following regions:
rectum, 0 to 10 cm; sigmoid, 10 to 30 cm; and descending colon/splenic flexure,
30 cm or more. If the lesion was in an anatomical region (eg, rectum, sigmoid)
that was not completely examined (or not examined at all) at the initial examination,
and the year 3 examination extended the coverage of that region, then the
lesion was considered to be detected possibly because of increased depth of
insertion. If the lesion was detected in a region of the colon that had been
previously completely examined with an adequate preparation, then the lesion
was considered to be detected in a previously examined area. For example,
if the depth of insertion were 50 cm at baseline and 55 cm at the year 3 examination,
and if a descending colon polyp were detected at year 3, then the polyp was
considered as detected because of increased depth of insertion because more
of the descending colon was examined at year 3. However, in the same example,
if the polyp at the year 3 examination were detected in the sigmoid colon,
then the lesion was considered detected in a previously examined area because
at the baseline examination the sigmoid colon had, by definition, been fully
Institutional review boards at each of the participating institutions
approved the PLCO protocol and participants provided written informed consent.
The publications subcommittee of the PLCO steering committee approved the
publication of this article.
P values for frequency comparisons between
2 groups were generated based on the χ2 test or the McNemar
test when year 0 vs year 3 results on the same participants were compared.
For all comparisons, P<.05 indicates statistical
significance. Multivariable logistic regression was used to assess the effect
of various factors on the likelihood of having any distal adenoma or advanced
distal adenoma. Factors included in the model were sex, age, body mass index,
education, smoking history, family history of colorectal cancer, previous
endoscopy, and result of the baseline screening. Individuals with a positive
year 3 screening examination who did not undergo diagnostic follow-up were
included in overall results but were excluded from analyses for which distal
adenoma status was required. Confidence intervals (CIs) for odds ratios (ORs)
were calculated based on Wald statistics. SAS statistical software, version
8.2 (SAS Institute Inc, Cary, NC), was used for all analyses.
Of 11 583 individuals without a polypoid mass or lesion on initial
FSG and eligible for repeat screening 3 years later, 9317 (80.4%) returned
(Table 1). The mean (SD) age at
randomization was 65.7 (4.0) years and 61.6% were men. Nearly 87% were white
and 73% had education beyond high school. Only 5.9% were current smokers and
10.1% reported a family history of colorectal cancer in a first-degree relative.
Slightly more than 40% self-reported undergoing an examination of the lower
bowel with sigmoidoscopy, colonoscopy, or barium enema in the 3 years prior
to study entry. At the initial FSG, 89.8% had insertion of the sigmoidoscope
to 50 cm or beyond and 57.3% had findings such as internal hemorrhoids or
diverticulosis. The characteristics of those who returned in comparison with
the 2266 individuals (19.6%) who did not return were similar except that nonreturnees
were moderately less educated (36.6% were college graduates or beyond vs 41.3%
in returnees), more likely to be current or former smokers (56.1% vs 50.6%
in returnees), and more likely to have had an inadequate FSG at baseline (22.6%
vs 11.2% in returnees).
The results of the repeat FSG examination, 3 years after the initial
examination, are shown in Table 2,
and a schematic diagram of the outcome of the sample is shown in Figure 1. Of 9317 returnees, 1292 (13.9%)
had a repeat FSG that was classified as abnormal suspicious, signifying that
a polyp or mass was detected. Men were more likely than women to have a polyp
or mass found at repeat screening (15.6% vs 11.1%; P<.001).
Inadequate examinations comprised 12.3% of the repeat screens and were more
frequent in women than in men (18.1% vs 8.6%; P<.001).
Among men, the rate of inadequate examinations was similar at the 2 points
(8.6% at repeat FSG vs 8.8% at initial FSG) but women had an increased rate
of inadequate examinations at year 3 (18.1% at repeat FSG vs 14.9% at initial
FSG; P<.001). The depth of insertion at the year
3 examination was similar to that at the baseline examination, with 86.7%
having an insertion to 50 cm or beyond. Of those with an abnormal suspicious
year 3 examination, 64.4% had 1 abnormal lesion identified, 19.7% had 2, 7.8%
had 3, and 8.1% had 4 or more abnormal lesions found. The largest polyp size,
estimated at the time of sigmoidoscopy by the examiner, was at least 1 cm
in 5.5%, between 0.5 and 0.9 cm in 21.6%, and 0.5 cm or smaller in 73.0%.
Of the 1292 individuals with an abnormal suspicious year 3 screening
sigmoidoscopy, diagnostic follow-up was available for 951 (73.6%). Eight hundred
forty-seven underwent colonoscopy and 104 underwent repeat FSG (Figure 1). The findings in the distal colon on sigmoidoscopy or
colonoscopy are presented in Table 3.
Overall, 30.1% were found to have an adenomatous polyp in the distal colon
and 0.6% had cancer in the distal colon (n = 6). Men were more likely than
women to have adenomas (32.4% vs 25.3%; P = .03).
A total of 22.1% had only hyperplastic polyps detected and 27.3% had no distal
lesion identified at colonoscopy or on repeat FSG. Of the 286 who had a distal
adenoma, 15.4% had an adenoma that was 1 cm or more in size, 14.0% had an
adenoma with tubulovillous or villous histology, and 2.4% had an adenoma with
high-grade dysplasia. Overall, 25.2% of individuals with a distal adenoma
had an advanced distal adenoma.
The cumulative number of individuals yielding adenoma, advanced adenoma,
or cancer in the distal and proximal colon is summarized in Table 4. In the distal colon, 292 (3.1%) of 9317 had an adenoma
or cancer. The yield of an advanced adenoma or cancer in the distal colon
was 78 (0.8%). Data in the proximal colon are available for 847 individuals
who underwent colonoscopy after an abnormal year 3 FSG. The yield for adenomas
and advanced adenomas in the proximal colon was lower than that for the distal
colon. The cumulative yield for adenoma in the entire colon was 4.1%, with
an advanced adenoma or cancer rate of 1.3%. Seven cancers were detected, of
which 6 were in the distal colon.
A detailed review of individuals with advanced distal adenomas was performed
to assess whether the lesions detected as a result of repeat sigmoidoscopy
at year 3 were detected because of increased depth of insertion at the second
examination or improved preparation, in contrast with detection in a portion
of the colon that had been previously examined. Of 72 with advanced distal
adenomas, only 14 (19.4%) of the diagnoses could possibly be attributed to
either increased depth of insertion or better preparation at the second examination.
Multivariable logistic regression of the factors associated with detection
of distal adenoma and distal advanced adenoma at 3-year follow up are presented
in Table 5. Men (OR, 1.7; 95%
CI, 1.3-2.2; P<.001) and current smokers (OR,
1.6; 95% CI, 1.0-2.5; P = .05) were more likely to
have distal adenomas at repeat examination. Family history of colorectal cancer
in a first-degree relative was associated with increased risk of advanced
distal adenomas (OR, 2.0; 95% CI, 1.1-3.7; P = .02),
as was an inadequate examination at baseline (OR, 2.7; 95% CI, 1.4-5.4; P = .004). A colon examination with sigmoidoscopy, colonoscopy,
or barium enema within 3 years prior to study entry was associated with a
decreased risk at the year 3 examination of any distal adenoma (OR, 0.7; 95%
CI, 0.6-0.9; P = .01) and an advanced distal adenoma
(OR, 0.4; 95% CI, 0.3-0.7; P = .002).
Table 6 presents a detailed
listing of the 7 cancers detected as a result of the year 3 sigmoidoscopy.
The detected cancers fall into 3 classifications: (1) cancer detected because
the depth of insertion on repeat sigmoidoscopy extended beyond that of the
initial sigmoidoscopy (case 3); (2) cancer detected because an abnormality
was detected at the second sigmoidoscopy (a distal marker) in a region previously
examined at the initial sigmoidoscopy, triggering a colonoscopy that led to
detection of a cancer (cases 1 and 7); and (3) cancer detected in a region
that had been previously examined at initial sigmoidoscopy (cases 2, 4, 5,
and 6). Cancers in cases 1, 3, and 7 might have been detectable with a colonoscopy
at the time of initial screening, although cases 3 and 7 had small lesions
at the time of detection. Similarly, in cases 4, 5, and 6, the cancers were
small and may represent lesions that grew to detectable size during the 3-year
period between examinations, but alternative explanations, such as evolution
from a flat adenoma or a missed lesion at initial sigmoidoscopy, cannot be
The incidence of adenoma or cancer in the distal colon 3 years after
a negative FSG was 3.1%. One quarter of the individuals with adenomas had
advanced adenomas, and 6 distal colon cancers were detected, for an advanced
distal lesion detection rate of 0.8%. Although it cannot be determined whether
these lesions were missed at the initial FSG or whether they developed over
the 3-year observation period between examinations, 80.6% of those with advanced
distal adenomas had lesions found in a portion of the colon that had been
adequately examined at the initial sigmoidoscopy. Regardless of whether these
were missed or new lesions, to our knowledge these data provide the first
representative estimate of what can be expected on repeat examination 3 years
after a negative FSG.
Screening examinations were performed in the context of the PLCO cancer
screening trial, a national randomized trial with broad geographic representation.
Participants were community-based volunteers who were asymptomatic at enrollment.
By protocol, they underwent repeat screening 3 years later, so repeat examination
was not dependent on clinical circumstances. Flexible sigmoidoscopy was performed
by trained nurses, certified internists, or specialists. The quality of the
examinations was good, as demonstrated by a depth of insertion of the sigmoidoscope
to more than 50 cm in more than 90% of the population at the baseline examination
and in more than 86% at the year 3 examination. The high rate of return for
repeat screening18 and the high levels of patient
satisfaction with sigmoidoscopy, when formally assessed,19 further
attest to the standards with which examinations were performed. Preliminary
data further suggest that nurses and physicians performed sigmoidoscopy with
These data have great importance in determining optimal screening intervals
and understanding the limitations of screening. The yield of cancer in the
distal colon at the baseline PLCO examination for individuals enrolled in
the same period as participants included in these analyses was 27 per 10 000
(data not shown) compared with a yield of cancer in the distal colon at the
year 3 examination of 6 of 9317 (6.4/10 000); thus, the ratio of cancer
yields at the 2 examinations was about 4.2:1.0. The yield of advanced distal
adenomas at the baseline evaluation was 2.5% (data not shown) vs a yield of
0.8% at 3 years after a negative sigmoidoscopy, giving a ratio of advanced
adenoma yield of 3.1:1.0. Thus, the yield for cancer and advanced adenomas
3 years after a negative sigmoidoscopy was one fourth to one third of what
was detected at the initial examination 3 years prior.
Recent studies of screening colonoscopy suggest that 1% to 2% of individuals
will have a proximal advanced adenoma or cancer detected by colonoscopy that
would have been missed with FSG.21,22 The
prevalence of advanced proximal neoplasia has fueled interest in screening
colonoscopy. However, colonoscopy as a screening examination is expensive,
and one of the variables that most influences its cost is the frequency of
its use.23 Strategies using colonoscopy as
a primary screening mode have advocated its use less frequently (eg, once
every 10 years).1 Although some organizations
have touted colonoscopy every 10 years as the "preferred" colorectal cancer
screening strategy,24 there are no observational
data examining the yield of a second colonoscopy 10 years after a negative
examination. Previous studies examining the yield after negative sigmoidoscopy
or colonoscopy are limited by small, unrepresentative samples6- 9,12- 14 or
variable follow-up based on clinical symptoms,10,14 making
it difficult to generalize the findings to colorectal cancer screening.11 It is difficult to predict how colonoscopy would
have performed had it been used instead of sigmoidoscopy. Colonoscopy would
have detected additional individuals with advanced proximal neoplasia, some
of which have not come to clinical presentation. Some of the distal cancers
and advanced adenomas detected at the year 3 examination might have been detected
at baseline with a longer initial depth of insertion or a better bowel preparation.
However, our analysis suggests that the vast majority of the advanced lesions
detected at year 3 would not have been detected at baseline, even if colonoscopy
had been used, because more than 80% of these lesions were detected within
reach of the initial sigmoidoscopy.
Our data are of concern because the 0.8% yield of advanced lesions on
repeat sigmoidoscopy after a negative examination is only moderately reduced
compared with the 1% to 2% yield of advanced proximal lesions that has encouraged
the use of screening colonoscopy. Furthermore, the only factor associated
with protection from detection of an advanced distal adenoma at 3-year follow-up
(OR, 0.4) was a lower gastrointestinal tract examination within the 3 years
prior to study entry. The implication is that more frequent examinations will
detect and prevent subsequent advanced lesions and thereby lessen morbidity.
If the yield on an interim examination after 3 years is relatively high, then
a longer interval between examinations, such as 5 or 10 years, may result
in more substantial morbidity and mortality. Studies of repeat examinations
after longer time intervals are needed. Whether these findings are translatable
to what would be found after a negative colonoscopy is not known. If they
are, then individuals undergoing colonoscopy once every 10 years may be at
increased risk for advanced findings if they wait 10 years for the next screening
We also found an increased likelihood of advanced distal lesions with
inadequate baseline examinations due to either poor preparation or less-than-optimal
depth of insertion. Our data support consideration for colonoscopy in patients
with inadequate sigmoidoscopy.
It is possible that patients might benefit from interval examinations
with FSG as opposed to less frequent examinations with colonoscopy. This may
be especially true for individuals between ages 50 and 65 years, whose risk
of proximal neoplasia is lower than that of those older than 65 years.25,26 Alternatively, screening methods
such as molecular stool testing27,28 or
virtual colonoscopy29 may be required during
the long intervals between colonoscopic screening to improve effectiveness.
In our sample, as in others,21,22 the
prevalence rate for advanced lesions in the proximal colon was a fraction
of that in the distal colon. In the screening colonoscopy study in the Veteran's
Administration population, 80% of the cancers were in the distal colon.21 This further supports consideration of more frequent
screening of the distal colon.
One limitation of this study is that participants were drawn from a
cancer screening trial that is overrepresented by more educated, more affluent,
and nonminority participants.30 As a result,
these data may not be applicable to specific minority or ethnic groups. Our
estimates for findings in the distal colon are conservative because only 951
of 1292 people with an abnormality underwent follow-up diagnostic testing.
However, 83.4% of the individuals who did not undergo follow-up testing had
lesions of 5 mm or smaller detected at the repeat FSG and, thus, are at low
risk of both advanced distal and proximal lesions.31 More
than 27% of individuals with a positive sigmoidoscopy had no distal lesion
on follow-up colonoscopy. These screens can be viewed as either false-positive
sigmoidoscopy or false-negative colonoscopy examinations. Sigmoidoscopy positivity
rates vary across examiners32,33 because
of variability in examiner threshold for deciding whether a bump should be
considered a polyp or not. For example, in a study of back-to-back FSG, 18.5%
had a polyp identified at the second examination when none was identified
at the first.34 Similarly, studies of tandem
colonoscopy show that lesions sized 5 mm or smaller can be missed up to 27%
of the time.16 Thus, variability in findings
at sigmoidoscopy or on follow-up colonoscopy after sigmoidoscopy, especially
for small lesions, is expected.
In conclusion, our results show that 3 years after a negative FSG, there
is a 0.8% incidence of advanced adenomas or cancer detectable in the distal
colon. 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.