Introduction
Colorectal cancer (CRC) is a major cause of cancer-related mortality and morbidity
in the Western world [1]. To reduce CRC incidence and mortality, CRC screening programs have been implemented
[2]
[3]. Screening via fecal immunochemical testing (FIT) is proven to be effective in reducing
CRC-related deaths [4].
In 2014 the FIT-based Dutch Bowel Cancer Screening Program (BCSP) was implemented
for individuals aged 55 to 75 years. After an unfavorable FIT result, patients are
invited for a colonoscopy to detect and resect (pre) cancerous lesions. This has resulted
in an increase in number of colonoscopies, polyp detection and resection and histological
assessments, leading to a substantial financial burden on the health care system [5].
The majority of polyps found during screening colonoscopy are small ( ≤ 10 mm) and
contain non-advanced histologic features, but in current clinical practice all polyps
are resected and sent for histological assessment, on which surveillance recommendations
are made. It has been seriously questioned whether histological evaluation of all
these small, diminutive lesions is worthwhile and more efficient and cost-effective
strategies should be implemented [6].
Optical diagnosis of colorectal polyps refers to “in vivo” estimation of histology
of the polyp by endoscopists using high-definition endoscopy in conjunction with (virtual)
chromoendoscopy [7]. Two strategies are proposed for implementation in clinical practice, but only if
the Preservation and Incorporation of Valuable endoscopic Innovations (PIVI) thresholds
are met [7]. First, the “resect and discard” strategy applies to diminutive (≤ 5 mm) colorectal
adenomatous polyps which are resected, but are not sent out for histological evaluation
(PIVI threshold: ≥ 90 % agreement between optical diagnosis and histological diagnosis
in determining the post-polypectomy surveillance interval). Second, the ‘diagnose
and leave’ strategy, where diminutive hyperplastic polyps in the rectosigmoid are
identified and left in situ (PIVI threshold: ≥ 90 % negative predictive value (NPV)
for optical diagnosis of diminutive adenomatous polyps) [8].
Up to now, data on optical diagnosis have been obtained mainly in study settings,
i. e. from expert centers with high-confidence optical diagnosis, as the PIVI guidelines
suggest. However, to actually implement these strategies, data from routine clinical
practice are needed. Here, we present the first detailed data from the Dutch Bowel
Cancer Screening Program (BCSP); a real-life but standardized endoscopy practice setting.
The aim of this study was to evaluate whether PIVI thresholds are met regarding a)
the diagnostic accuracy of optical diagnosis for diminutive polyps and regarding b)
the “resect and discard” and “diagnose and leave” strategy, within the BCSP in a defined
region of the Netherlands, South Limburg, representing our national data [9]
[10].
Patients and methods
Patients and centers
Longitudinal data collection was performed in the four endoscopy centers in South-Limburg
region of the Netherlands: one academic center and three regional endoscopy units.
All endoscopic and histological data of FIT-unfavorable participants (55–75 years)
who underwent colonoscopy within the context of the Dutch BCSP from February 2014
to August 2015 were collected. A threshold of 15 µg Hb/g feces was considered FIT
unfavorable (FOB gold, Sentinel, Milan, Italy) in the first six months but was raised
to 47 Hb/g because of limitations in endoscopy capacity [5].
We included all patients with index colonoscopies fulfilling the quality criteria
in the screening program (cecal intubation and adequate bowel preparation defined
as Boston Bowel Preparation Score [BBPS] ≥ 6) in this retrospective analysis. This
trial is registered in the Netherlands Trial Registry (NTR4844) and the METC of Maastricht
University Medical Center assigned approval for the prospective colonoscopy database
(Number: 14-4-046). Need for informed consent was waived by the Institutional Review
Board.
Endoscopists and equipment
European guidelines for quality assurance in CRC screening have been set [3]. In the Netherlands, endoscopists have to be certified before being allowed to participate
in the BCSP [11]
[12].
To be admitted to the Dutch BCSP, endoscopists should have performed at least 300
colonoscopies and over 50 polypectomies per year. Furthermore, quality measures have
been set and are evaluated [11]. In addition, endoscopists are required to register 100 consecutive colonoscopies
with corresponding quality indicators. Then, a theoretical e-learning module should
be accomplished and colonoscopic skills are evaluated in live practice setting and
via videos [12]. All endoscopists in this study fulfilled the quality measures for the screening
program as described above but they received no specific additional training regarding
optical diagnosis of colorectal polyps.
Because the data are retrieved from a clinical practice setting, endoscopists performed
standard care and were not informed about the study. All parameters currently included
in the standardized endoscopy-report for the Dutch BCSP were obtained, assuming that
all lesions found have been described in this report, as this is current clinical
practice.
Among others, location, size, Paris-classification and predicted histology (optical
diagnosis) were reported and the removed polyps were collected and sent in for histological
evaluation. The classification options for estimated histology were: adenomatous polyp,
hyperplastic polyp, sessile serrated lesion, carcinoma and other. No specific classification
system (NICE, WASP) nor the confidence of the estimated histology are included in
the standardized endoscopy-report. Therefore, these data were not available for evaluation.
High-definition white light colonoscopy (HD-WLE) was used in all endoscopy units and
also (virtual) chromoendoscopy was available and used upon discretion of the endoscopist.
All colonoscopies were performed using endoscopic equipment containing virtual chromoendoscopy,
either I-scan (Pentax Europe) used in one endoscopy unit or NBI (Olympus, Tokyo, Japan),
used in the three other endoscopy units. The use of image-enhancement was not systematically
included in the endoscopy report. To obtain an estimation on the use of image-enhancement
endoscopy (IEE), we reviewed the photo documentation to see whether image-enhancement
was captured in the photos. The use of IEE is scored for every polyp, and in case
no photo was available or in case of more polyps in the same region, there had to
be at least five (consecutive) photos where IEE was used for a positive score.
Colonoscopy
Standard bowel preparation regimens were used with polyethylene glycol solution containing
ascorbic acid or Picosulfate sodium (Moviprep Norgine GmbH, Marburg, Germany or Picoprep®,
Ferring GmbH, Kiel, German y). After introduction to the cecum, the quality of bowel
preparation was scored using the Boston Bowel Preparation Score (BBPS), where 3 is
the maximum score for each segment (right, transverse, left) resulting in a total
maximum score of 9 [13]. BBPS score of ≥ 2 for each segment and ≥ 6 in total is considered adequate bowel
preparation.
Histology
All resected lesions were sent to the local pathology department and processed according
to standard protocol. All pathologists had been trained and authorized for participation
in the BCSP [11]. The Vienna criteria for gastrointestinal epithelial neoplasia were used for classifying
the biopsies, and the diagnosis by histology was used as reference [14].
Outcome measures and statistical analysis
The outcome was the diagnostic accuracy, i. e. overall accuracy, sensitivity, specificity,
NPV and positive predictive value (PPV) between optical diagnosis and histological
diagnosis of diminutive polyps, where histological diagnosis was used as reference
standard. All polyps ≤ 5 mm with both optical diagnosis and histological evaluation
were included in the analysis. To clarify the results, the data were dichotomized
into in adenomas versus all other polyps and hyperplastic polyps versus all other
polyps. Cross tables were made allowing to calculate the overall accuracy (percentage
of congruent pairs), sensitivity, specificity, NPV and PPV.
To take into account use of IEE, a sensitivity analysis is performed, using Chi-square
test, for the use of IEE and optical diagnosis.
To analyze whether diagnostic accuracy differs between the endoscopy units Chi-square
test was used. We performed a sensitivity analysis to measure the effect of clustering
(i. e. multiple lesions per patient), by calculating the values of the first primary
outcome with and without multilevel correction.
The other outcome parameter was the post-polypectomy surveillance intervals based
on optical diagnosis, according to a) Dutch Surveillance Guidelines [15] b) European post-polypectomy colonoscopy surveillance guidelines [16] and c) American Guidelines for surveillance after polypectomy [2].
Surveillance intervals were determined per patient based on a combination of optical
diagnosis (for diminutive polyps) and histology, where histology was used as reference.
For each individual patient, all lesions (diminutive but also larger lesions) were
taken into account when determining the interval of surveillance.
These outcomes are chosen to evaluate whether two strategies can be implemented in
clinical practice. The PIVI threshold for implementing the “resect and discard” strategy
is ≥ 90 % agreement between optical diagnosis and histological diagnosis in determining
the post-polypectomy surveillance interval. For implementation of the “diagnose and
leave:” strategy the PIVI threshold that should be met is ≥ 90 % NPV for optical diagnosis
of diminutive adenomatous polyps.
Statistical analyses were performed using IBM SPSS Statistics for Windows Statistical
Package for Social Sciences (version 22, IBM Corp, Armonk, New York, United States)
and R-statistics was used for the sensitivity analysis (R Foundation for Statistical
Computing, Vienna, Austria).
Results
Patient characteristics
Between February 2014 and August 2015, 2,470 participants in the Dutch BCSP with an
unfavorable FIT result underwent an index colonoscopy with polypectomy in the South
Limburg region. A total of 140 cases were excluded due to insufficient colonoscopy
quality (no cecal intubation [n = 51], inadequate bowel preparation [n = 19] or both
[n = 70]) ([Fig. 1]), resulting in 2330 patients eligible for this study. In [Table 1] characteristics of the included patients are described.
Fig. 1 Flowchart of the included patients and polyps.
Table 1
Characteristics of the included patients (n = 2330).
|
Age (mean, SD), years
|
68 (5)
|
|
Gender (female, n (%))
|
889 (39)
|
|
ASA Classification, n (%)
|
|
|
801 (34)
|
|
|
1441 (62)
|
|
|
88 (4)
|
|
|
1 (0)
|
|
Boston Bowel Preparation Score (mean, SD)[1]
|
9 (1)
|
|
Cecal withdrawal time (mean, SD), minutes
|
17 (11)
|
1 Only patients with cecal intubation and BBPS ≥ 6 were included
Fifteen endoscopists participated in this study (n = 5 from the academic center, n = 10
from regional endoscopy units). All had extensive colonoscopy experience (endoscopy
experience in years: mean 10.9 years, SD 5.7; range 3 to 22 years) and had been certified
for the national CRC screening program. The number of BCSP colonoscopies performed
per endoscopist in the current study varied (mean 165 colonoscopies, SD 119; range
11 to 363).
Lesion characteristics
In total, 7,369 polyps were found; 1,573 were > 10 mm and 2,304 with size 6 to 10 mm.
From the total of 3,492 diminutive polyps, both optical diagnosis (n = 196 missing)
and histological data (n = 160 missing) needed to be available (n = 108 both missing),
resulting in 3028 diminutive lesions that were included ([Fig. 1]). Endoscopic characteristics of these polyps are shown in [Table 2]. Median size of diminutive polyps was 4 mm, 40 % of the polyps were located in rectosigmoid
(n = 1222). Histology showed that 67 % were adenomatous and 19 % hyperplastic. In
the 1- to 5-mm group, a total of three carcinomas were detected and 15 adenomas showed
high-grade dysplasia ([Table 2]).
Table 2
Endoscopic and histologic characteristics of diminutive lesions and accuracy per center.
|
Lesions in colon and rectum
|
Lesions in rectosigmoid
|
|
Number of diminutive lesions
|
3028
|
1222
|
|
Polyp size (mean, SD) in mm
|
4 (1)
|
4 (1)
|
|
Polyp size (n, %)
|
|
|
544 (18)
|
192 (16)
|
|
|
2484 (82)
|
1030 (84)
|
|
Paris classification (n, %)[1]
|
|
|
235 (8)
|
118 (10)
|
|
|
2477 (82)
|
985 (81)
|
|
|
264 (9)
|
95 (8)
|
|
|
15 (0)
|
4 (0)
|
|
|
37 (1)
|
20 (1)
|
|
Histology (n, %)
|
|
|
2038 (67)
|
602 (49)
|
|
|
1964
|
572
|
|
|
1
|
1
|
|
|
73
|
29
|
|
|
106 (4)
|
41 (3)
|
|
|
563 (19)
|
439 (36)
|
|
|
3 (0)
|
2 (0)
|
|
|
99 (3)
|
48 (4)
|
|
|
222 (7)
|
92 (8)
|
|
Dysplasia (n, %)
|
|
For adenomas
|
|
|
2022 (99.2)
|
589 (97.8)
|
|
|
15 (0.7)
|
12 (2.0)
|
|
|
1 (0.1)
|
1 (0.2)
|
|
For sessile serrated lesions
|
|
|
31 (29.2)
|
10 (24.4)
|
|
|
71 (67.0)
|
30 (73.2)
|
|
|
4 (3.8)
|
1 (2.4)
|
|
Diagnostic accuracy per endoscopy center
(n of polyps, % correctly estimated lesions)
|
Adenomas in colon and rectum
|
Hyperplastic polyps in rectosigmoid
|
|
|
839 (77)
|
339 (72)
|
|
|
1007 (74)
|
397 (70)
|
|
|
928 (77)
|
386 (73)
|
|
|
254 (76)
|
100 (70)
|
1 There were no Paris II-c lesions, since these are not considered amenable to optical
diagnosis.
2 No significant difference in overall diagnostic accuracy between the centers for
adenomas in colon (P = 0.393) or hyperplastic polyps in rectosigmoid (P = 0.769).
Performance of optical diagnosis
Optical diagnosis for diminutive adenomas in the colon and rectum showed a diagnostic
accuracy of 76 % (95 % CI 74–77) compared to histological diagnosis. The NPV for adenomatous
histology was 69 % (95 % CI 66–73) ([Table 3]).
Table 3
Optical diagnosis versus histological evaluation of diminutive polyps.[1]
|
Lesions in colon and rectum (n = 3028)
|
|
Adenomas (n = 2038)[2]
|
Hyperplastic polyps (n = 563)[2]
|
|
Overall accuracy (95 % CI)
|
76 % (74–77)
|
79 % (77–80)
|
|
Sensitivity (95 % CI)
|
90 % (88–91)
|
48 % (44–53)
|
|
Specificity (95 % CI)
|
47 % (44–50)
|
85 % (84–87)
|
|
Positive Predictive Value (PPV) (95 % CI)
|
78 % (76–79)
|
43 % (39–47)
|
|
Negative Predictive Value (NPV) (95 % CI)
|
69 % (66–73)
|
88 % (86–89)
|
Table 3 (Continuation)
Optical diagnosis versus histological evaluation of diminutive polyps.[1]
|
Lesions in the rectosigmoid (n = 1222)
|
|
Adenomas (n = 602)[2]
|
Hyperplastic polyps (n = 439)[2]
|
|
Overall accuracy (95 % CI)
|
72 % (69–74)
|
71 %(69–74)
|
|
Sensitivity (95 % CI)
|
89 % (86–92)
|
54 % (49–59)
|
|
Specificity (95 % CI)
|
55 % (51–59)
|
81 % (78–84)
|
|
Positive Predictive Value (PPV) (95 % CI)
|
66 % (62–69)
|
61 % (56–66)
|
|
Negative Predictive Value (NPV) (95 % CI)
|
84 % (80–87)
|
76 % (73–78)
|
1 Diagnostic performance for different polyp subtypes (hyperplastic and adenomatous
lesions) were calculated by dichotomizing outcomes, where histological outcome is
used as reference.
2 These numbers represent the total number of adenomas and hyperplastic polyps using
histological evaluation, i. e. the reference.
In the rectosigmoid, a total of 1222 diminutive lesions were found, the NPV for adenomatous
histology was 84 % (95 % CI 80–87). For hyperplastic polyps in the rectosigmoid the
NPV was 76 % (95 % CI 73–78), the PPV was 61 % (95 % CI 56–66) and overall accuracy
was 71 % (95 % CI 69–74) ([Table 3]).
A total of 150 polyps in rectosigmoid (12.3 % of the total) were optically misdiagnosed
as hyperplastic. In 5.1 % and 1.9 % of the cases, an adenoma or sessile serrated lesion,
respectively, would have been left in place (5.3 % other/no abnormality) ([Table 4]).
Table 4
Specification of the polyps incorrectly estimated as hyperplastic polyp in the rectosigmoid
region.
|
Pathology evaluation
|
Number
|
% from incorrectly estimated hyperplastic polyps
|
% from total polyps in rectosigmoid
|
|
Total
|
150[1]
|
100 %
|
12.3 %
|
|
Adenoma
|
62
|
41.3 %
|
5.1 %[2]
|
|
|
59
|
|
|
0
|
|
|
3
|
|
Serrated lesions
|
23
|
15.3 %
|
1.9 %[2]
|
|
|
22
|
|
|
1
|
|
Other
|
23
|
15.3 %
|
1.9 %
|
|
|
20
|
|
|
1
|
|
|
2
|
|
No abnormality
|
42
|
28.0 %
|
3.4 %
|
1 A total of 150 polyps in rectosigmoid (12.3 % of the total) were optically misdiagnosed
as hyperplastic.
2 In 5.1 % and 1.9 % of the cases, an adenoma or serrated lesion, respectively, would
have been left in place.
For the optically misdiagnosed lesions (n = 139/150 photo documentation available),
no significant difference was found with regard to use of IEE (P = 0.620).
Diagnostic accuracy for diminutive adenomas in the colon and rectum ranged from 74
to 78 % (P = 0.393) between the four endoscopy units and regarding hyperplastic lesions in the
rectosigmoid diagnostic accuracy ranged from 70 to 73 % (P = 0.769) ([Table 2]).
Overall diagnostic accuracy between the 15 endoscopists ranged from 69 % to 87 %.
From 2576 polyps photo documentation was available. Image enhancement had been documented
by endoscopy photos in 36.9 %, where in the majority of the cases I-scan was used.
There was no significant difference between the use of IEE and the correct optical
diagnosis for both adenomas in the colon and rectum (P = 0.612) and for hyperplastic polyps in the rectosigmoid (P = 0.842).
The sensitivity analysis to correct for clustering (i. e. multiple lesions per patient)
showed similar results. (Data not shown.)
Surveillance intervals
In [Table 5] results of the surveillance intervals are given. Surveillance intervals have been
calculated at patient level, meaning that if only diminutive polyps were found the
surveillance interval is based on optical diagnosis solely, whereas if additional
polyps (> 5 mm) were found, the histology of these non-diminutive polyps determined
the surveillance intervals. For the “resect and discard” strategy agreement for the
Dutch, European, and American guidelines was 90.6 %, 91.2 % and 90.9 % respectively.
Approximately 6.0 % would have received a shorter surveillance interval based on optical
diagnosis, while in 2.8 % to 3.3 % of the cases a longer surveillance interval would
have been recommended.
Table 5
Surveillance intervals based on optical diagnosis vs. histology, according to different
guidelines (NL, EU, USA) and applying the “resect and discard” scenario.
|
Resect and discard strategy
(Optical diagnosis for adenomatous polyps in the entire colon)
N = 2330 patients
|
|
Agreement between optical diagnosis and histology
|
Surveillance
earlier
|
Surveillance
later[1]
|
|
Dutch guideline
|
90.6 %
N = 2110
|
6.2 %
N = 144
|
3.3 %
N = 76
|
|
European guideline
|
91.2 %
N = 2126
|
5.9 %
N = 137
|
2.9 %
N = 67
|
|
American guideline
|
90.9 %
N = 2119
|
6.2 %
N = 145
|
2.8 %
N = 66
|
1 This includes also the patients who receive no surveillance according to optical
diagnosis. The number of patients who would receive no surveillance are for the Dutch
guideline 36/76 patients, for the European guideline 36/67 patients and according
to the American guideline 4/66.
A detailed overview of the surveillance intervals for the “resect and discard” and
“diagnose and leave in place” strategies using different guidelines is presented in
Supplementary Table 1 and Supplementary Table 2.
Discussion
We have evaluated the accuracy of optical diagnosis of diminutive polyps, as well
as the scenarios for “resect and discard” and “diagnose and leave” in the clinical
endoscopy practice setting of the Bowel Cancer Screening Program (BCSP) in the Netherlands.
Optical diagnosis of diminutive adenomatous polyps in the rectosigmoid showed 72 %
diagnostic accuracy and 84 % NPV: thus, the PIVI thresholds were not met.
When applying the “resect and discard” scenario, agreement on surveillance intervals
between optical and histological diagnosis applying the Dutch, European and American
surveillance guidelines was 90.6 %, 91.2 % and 90.9 % respectively. Therefore, at
group level, the PIVI thresholds (≥ 90 % agreement) concerning surveillance strategies
were met.
Given the substantial amount of research focusing on optical diagnosis and the potential
cost savings, this is an important and clinically relevant topic [17]
[18]. However, results of studies assessing optical diagnosis of small and diminutive
polyps vary considerably. So far, data have been obtained predominantly in well controlled
study settings, where endoscopists were additionally trained in recognition and characterization
of lesions and had been instructed on the systematic use of image-enhancement. Baseline
characteristics of the diminutive lesions in our study are within the range of variation
reported in recent literature, and are therefore representative for national and global
data [19]
[20].
When evaluating published data from additionally trained endoscopists, the NPV for
optical diagnosis of adenomas in the rectosigmoid varies from 82.0 % to 94.7 % in
studies where narrow-band imaging (NBI) was used [21]. Ladabaum et al. [22] showed that while only 25 % of the trained endoscopists used NBI, polyps were assessed
with over 90 % accuracy.
Image enhancement for optical diagnosis of diminutive polyps is considered to be beneficial,
but remains an item of discussion since several studies have not shown significant
differences in accuracy for optical diagnosis with image enhancement compared to HD-WLE
[23]
[24]
[25]. In our study, reflecting daily endoscopy practice, use of image-enhancement in
addition to HD-WLE was left at the discretion of the endoscopist. In 36.9 % use of
image-enhancement was photo-documented and no significant differences were found in
optical diagnosis with or without use of IEE.
Experience and additional training of endoscopists may substantially add to accuracy
of optical diagnosis. Endoscopists working in academic centers obtain better results
in optical diagnosis compared to endoscopists working in community practices [22]. Indeed, in a surveillance setting in non-academic centers without additional training,
Kuiper et al. [26] noted low sensitivity (77.0 %) and specificity (78.8 %) for optical diagnosis.
In our study, performance of academic and regional centers with respect to optical
diagnosis was in the same range. Concerning surveillance intervals, in previous studies,
19 % inaccuracy in determining surveillance intervals based on optical diagnosis has
been reported [26]. It should be noted that surveillance intervals were calculated on patient level,
therefore, all polyps (diminutive but also larger polyps) were taken into account,
taking into account that intervals are affected mostly by the larger polyps. Therefore,
optical misdiagnosis of smaller polyps can be overruled by the presence of larger
polyps. This raises the question whether surveillance interval is the most appropriate
criterium when deciding on diminutive polyps. It does however perfectly represent
the impact of the guidelines used in current clinical practice.
A recent Dutch study from Vleugels et al. has shown that at group level in a selected
population of endoscopists after additional training, optical diagnosis of diminutive
polyps (with high-confidence) in the Dutch FIT-based CRC screening setting using narrow-band
imaging (NBI) met the ASGE PIVI thresholds [20]. However, at individual level, only 59 % of the additionally trained endoscopists did meet these PIVI thresholds.
These authors showed that selected endoscopists, additionally trained by a validated
training module on NICE [27] and WASP [28] were able to diagnose neoplastic lesions (with high-confidence) using NBI in the
rectosigmoid with pooled NPVs of more than 90 % [20]. In addition, they were also able to accurately recommend surveillance intervals
based on optical diagnosis [20]. When interpreting these data, it should be noted that these endoscopists represent
an expert group, of which endoscopists were only allowed to participate after passing
an additional exam (≥ 90 % diagnostic accuracy (same as in PIVI)) [20]. Therefore, the results of that study cannot be extrapolated directly to community
practice. On the other hand, Vleugels et al. [20] have clearly shown that optical diagnosis may become feasible in a special setting
in which endoscopist training and feedback is incorporated.
In a study by Schachschal et al. performed in a screening setting, optical diagnosis
had an accuracy of only 71.1 % and NPV of 59.3 % [29]. Our results compare favorably with that study with NPV for hyperplastic polyps
in the rectosigmoid and for adenomas in the colon of respectively 76 % and 69 %. The
agreement on surveillance intervals in our study reached an accuracy of over 90 %,
while data from the Schachschal et al. study cannot be retrieved from the manuscript
[29].
To implement these strategies in clinical practice, costs should be considered. Using
simulation modelling, optical diagnosis in the Dutch BCSP appears to save costs without
decreasing program effectiveness when compared with current histology analysis of
all diminutive polyps [30]. In line with these modelling data, Hassan et al. have already shown that the “resect
and discard” strategy for diminutive polyps detected during screening indeed results
in economic benefit without impact on program efficacy [6]. Applying these strategies may not only result in cost savings but also in a reduction
of risks of polypectomies and of patient discomfort.
If lesions are left in situ (i. e. “diagnose and leave”’ scenario), an incorrect optical
diagnosis may have significant impact. In our study twelve percent of the rectosigmoid
lesions was estimated as hyperplastic but contained other histology (i. e. adenomas
and serrated polyps). When the lesions are removed (i. e. “resect and discard” scenario),
the impact of incorrect optical diagnosis is limited.
High-risk lesions found in our study (3 carcinomas and 15 lesions with high-grade
dysplasia) should be considered carefully. Here, evaluation of treatment and resection
margins is of importance, and they should receive stricter follow-up.
Several strengths of our study need to be acknowledged. First, we evaluated the efficacy
of the optical diagnosis strategy within a) the structured setting of the nationwide
Bowel Cancer Screening Program b) regular endoscopy practices where all participating
endoscopists were qualified and accredited for performing colonoscopies for the Dutch
FIT-based BCSP [12], but without additional training or selection for competency in optical diagnosis.
We prospectively collected data from four endoscopy units (both academic and regional)
in South Limburg (the Netherlands). The results therefore reflect daily clinical practice
in the Netherlands in the first years of implementation of the BCSP.
Several limitations need to be acknowledged as well. Since standardized endoscopy
reports are used for data collection, some detailed information is lacking. Therefore,
the results of this study should be interpreted with caution. First, the level of
confidence with which an endoscopist rates his/her optical diagnosis is relevant.
A meta-analysis from 2015 showed that estimations with high-confidence are more likely
to be correct [7]. In our real-life study endoscopists neither were asked for nor included the level
of confidence in the standard endoscopy-report and we were therefore not able to assess
the level of confidence for optical diagnosis. Second, image-enhancement was used
upon discretion of the endoscopist, but the specific use per polyp was not reported.
Based on photo-documentation, image-enhancement was used in at least 36.9 % of endoscopies.
To improve performance and to allow implementation of optical diagnosis in the setting
of a national BCSP, essential steps need to be taken: 1) for equipment, standard use
of high-definition white light endoscopy with additional image enhancement; 2) for
endoscopists, additional training and monitoring of individual performance; 3) standard
use of optical classification systems (e. g. NICE or WASP); 4) inclusion of “the level
of confidence in optical diagnosis” of the endoscopist in the optical diagnosis algorithm;
and 5) photo documentation and archiving [31]
[32].
Implementation of optical diagnosis strategy in clinical practice remains challenging
[31]. A simplified approach has been suggested by Atkinson and East [33]; the DISCARD-lite strategy where all diminutive polyps proximal to rectosigmoid
junction are assumed premalignant and therefore “resect and discard” is applied, while
hyperplastic polyps in the rectosigmoid can be left in situ. A recent study by von
Renteln et al. indicates that this simplified combined optical and location-based
strategy may help to overcome current challenges in the implementation of the ‘resect
and discard’ strategy [34].
In the near future an important role for artificial intelligence (AI) in optical detection
and characterization of diminutive polyps is foreseen, thus reducing or even eliminating
endoscopist inter-observer variability. Several computer-aided detection and characterization
systems and algorithms are being developed with promising preliminary data such as
a NPV for identification and classification of diminutive rectosigmoid adenomas ranging
from 91.5 % to 97 % [35]
[36]
[37]
[38]. More extensive research in larger clinical trial settings is necessary to confirm
and expand on these results.
Based on our data from regular endoscopy care in the bowel cancer screening program,
we cannot recommend leaving diminutive rectosigmoid polyps in place. On the other
hand, the thresholds for the “resect and discard” strategy, i. e. agreement on post-polypectomy
surveillance intervals were met. Implementation of this strategy can therefore be
considered. These results, however, need to be validated, in a setting where the above
mentioned steps have been implemented (i. e. standardized and structural use of level
of confidence and use of IEE).
Conclusion
To conclude, our study representing current clinical practice in the Dutch BCSP practice
on optical diagnosis of diminutive polyps showed that accuracy of predicting histology
remains challenging, and risk of incorrect optical diagnosis is significant. Therefore,
it is too early to safely implement these strategies. It remains to be determined
whether optical diagnosis will structurally meet the PIVI criteria in routine clinical
endoscopy practices.
