Detection rates of adenomas, advanced adenomas, and colorectal cancers among the opportunistic colonoscopy screening population: a single-center, retrospective study : Chinese Medical Journal

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Original Article

Detection rates of adenomas, advanced adenomas, and colorectal cancers among the opportunistic colonoscopy screening population: a single-center, retrospective study

Gong, Yan1; Zheng, Yansong2; Wu, Rilige3; Liu, Miao4; Li, Hong1; Zeng, Qiang5

Editor(s): Hao, Xiuyuan; Jia, Rongman

Author Information
Chinese Medical Journal ():10.1097/CM9.0000000000002435, January 25, 2023. | DOI: 10.1097/CM9.0000000000002435

Abstract

Introduction

Colorectal cancer (CRC) is the fifth most common cancer worldwide, with an estimated 1.88 million new cases in 2020.[1-4] The incidence rate varies widely in different regions of the world. In recent years, due to lifestyle changes and the growing elderly population as the living standards improve, the incidence of CRC in China has been increasing.[5] In 2020, colorectal cancer had an estimated 0.56 milion new cases and 0.29 million deaths in China, accounting for 29.97% and 31.99% of global cases, respectively.[4]

Most CRCs arise from non-cancerous, adenomatous polyps. CRC screening programs aim to intervene in the cancer progression process by the detection and subsequent removal of polyps before they progress to cancer and by early detection of CRCs in asymptomatic individuals.[6] Screening for CRC is cost-effective.[7] Several screening methods are available, including fecal occult blood test (FOBT), fecal immunochemical test (FIT), computed tomography (CT), sigmoidoscopy, and colonoscopy,[8] in which colonoscopy is a necessary follow-up for positive screening. Therefore, colonoscopy has become the preferred screening method for the detection and prevention of CRC in individuals at average risk and is recommended by many medical associations.[9,10] Optimizing the quality of CRC screening is necessary to improve its level. The adenoma detection rate (ADR) is one of the best indicators to measure the quality of colonoscopy.[11] In addition, the detection rate of serrated adenoma is also closely related to the quality of colonoscopy.[12]

The age of 50 years has long been the starting age for colonoscopy screening based on the increase in CRC prevalence at 60 years old, but the prevalence of CRC is now declining among older adults and increasing rapidly among young American adults.[3] Recently, the American Cancer Society proposed that the age of initiation for CRC screening among the general average-risk population should be reduced from 50 to 45 years old independent of gender,[13] while another study reported that the prevalence of advanced adenomas (AAs) and CRC in men was higher than that in women (7.96% vs. 4.65% for AA and 1.5% vs. 0.7% for CRC, respectively).[14] Although a study from China showed that the detection rates of adenomas and AAs gradually increased with age and were higher among men when compared with those of women in large-scale population-based CRC screening programs,[15] opportunistic colonoscopy screening for CRC among an asymptomatic average-risk population has been limitedly reported in China. The recent development of painless colonoscopy has improved the comfort of endoscopy, making it an important part of health examinations.

In the present study, we reported the detection rates of adenomas, AAs, and CRCs in different age groups of men and women and the number needed to screen (NNS) for them. We aim to provide more evidence for CRC screening in the average-risk population in China.

Methods

Ethical approval

The study protocol was approved by the Ethics Committee of the People's Liberation Army General Hospital, Beijing, China (No. S2021-636-01). Written informed consent was obtained from each enrolled individual.

Study population

This single-center, retrospective study included data of healthy individuals aged 17 to 85 years who underwent colonoscopies and health examinations at the Health Management Research Institute of People's Liberation Army General Hospital from January 2013 to December 2019. A total of 53,943 participants were enrolled in this study. The population was mainly from northern China, with the majority being Han Chinese. Questionnaires were sent before the health check, which included uncomfortable symptoms and medical history. At the outset, we excluded subjects with symptoms in the lower digestive tract, including melena, hemafecia, abdominal pain, diarrhea, constipation, and changes in defecation habits. Among the participants, those with postoperative follow-ups (n = 336) or at increased risk for CRC, including a personal or family history of CRC, inflammatory bowel disease, weight loss, anemia and bleeding (n = 455), were excluded. Finally, a total of 53,152 consecutive, asymptomatic subjects were included.

Colonoscopy procedure

All colonoscopies were performed by experienced digestive endoscopists (attending physician or above with >5 years of endoscopic experience). Each of them had performed at least 1000 colonoscopies. The examination was performed with standard sedation of the combination of pethidine and midazolam, or propofol alone given by the anesthesiologist. Subjects were given polyethylene glycol for bowel preparation together with instructions for use. A complete examination was defined as an endoscope reaching the cecum as documented by a picture of the ileocecal valve. All colorectal lesions found were documented for their site and size (measured by biopsy forceps that opened up to 7 mm). The withdrawal duration of the colonoscopy procedure was at least 6 min to minimize the chance of missing lesions. An incomplete examination was excluded from the analysis.

The Boston Bowel Preparation Scale was used for colonoscopy quality evaluation. The quality of bowel preparation was graded as good (no or small volume of clear liquid, with >95% of the surface observable), fair (between good and poor), and poor (presence of semisolid stool that could not be suctioned or washed away, and <90% of the surface observable).

Result determination and quality control

All abnormal findings found during colonoscopy were confirmed by pathological examination, and standardized pathological results were completed in accordance with the latest clinical guideline (World Health Organization Classification of Digestive Tumors: the Fourth Edition). Advanced colorectal adenoma was defined as the presence of adenoma >1 cm in diameter, high-grade dysplasia, or villous architecture. Serrated adenoma included sessile serrated adenoma/polyp (SSAP) and traditional serrated adenoma (TSA) in this study. In cases with multiple adenomas, we reported the information on the highest malignancy, and in cases with two or more adenomas of the same size, we reported the information on the farthest one. The proximal colon is considered to include all segments of the splenic curvature and above, while the distal colon is considered to include the descending colon, sigmoid colon, and rectum segments below the splenic curvature.

Data collection

All data, including colonoscopy results and histopathological analyses, were recorded and transferred to the study database using an electronically signed form along with the participants’ medical records. Each participant has a unique identification code for tracking and analyzing the relevant materials of all individuals.

Statistical analysis

The general characteristics were described as mean ± standard deviation (SD) for normally distributed continuous variables and as frequency (percentage) for categorical variables. We compared these characteristics between men and women using chi-squared test.

For the purpose of interpretation, the age groups were defined according to a 5-year period, starting at the age of <40 years, and the detection rates of adenomas, AAs, or CRCs were computed. The detection rate, NNS, and corresponding 95% confidence interval (CI) for men and women were also computed. We compared the potential differences between men and women with respect to age. All statistical analyses were performed using STATA statistical software, version 10 (http://www.stata.com/stata10/). All tests were double-sided, and a P value of <0.05 was considered statistically significant difference.

Results

General characteristics and colonoscopy findings

As shown in Table 1, a total of 53,152 subjects, 17,926 women (33.73%) and 35,226 men (66.27%), were included in the final analysis. The average age was 50.0 years (SD, 9.0 years) for women and 48.8 years (SD, 8.5 years) for men.

Table 1 - General characteristics of 53,152 individuals receiving colonscopic screening.
Factors Total Men Women χ 2 P values
Age groups (years) 53,152 35,226 (66.27) 17,926 (33.73) 323.53 <0.001
 <40 6119 4270 (69.78) 1849 (30.22)
 40–44 8499 5968 (70.22) 2531 (29.78)
 45–49 12,601 8510 (67.53) 4091 (32.47)
 50–54 12,830 8447 (65.84) 4383 (34.16)
 55–59 7017 4519 (64.40) 2498 (35.60)
 60–64 3860 2268 (58.76) 1592 (41.24)
 65–69 1696 941 (55.48) 755 (44.52)
 70–74 400 238 (59.50) 162 (40.50)
 ≥75 130 65 (50.00) 65 (50.00)
Colon polyps
 Mini- 10,268 7624 (74.25) 2644 (25.75) 362.22 <0.001
 Multi- 5915 4981 (84.21) 934 (15.79) 957.89 <0.001
Colorectal cancers 313 201 (64.22) 112 (35.78) 0.60 0.440
Other benign lesions 4382 2798 (63.85) 1584 (36.15) 12.53 <0.001
No abnormalities 32,811 19,862 (60.53) 12,949 (39.47) 1.3e+03 <0.001
Data are expressed as n or n (%).

Bowel preparation was good in 66.31% (35,245), fair in 26.76% (14,224), and poor in 6.93% (3683) of subjects. Those with poor bowel preparation were required to prepare for the second colonoscopy to meet the criteria for clinical diagnosis. Only six individuals developed post-polypectomy bleeding, which were resolved after endoscopic therapy by clipping. No individuals showed bowel perforation.

The findings included colon polyps in 30.45% of individuals (16,183), CRC in 0.59% (313), and other benign lesions in 8.24% (4382). No abnormalities were found in 61.73% of colonoscopies (n = 32,811). The detection rates of mini-colonic polyps and multiple colonic polyps were both higher in men compared with those of women (21.64% [7624/35,226] vs. 14.75% [2644/17,926] and 14.14% [4981/35,226] vs. 5.21% [934/17,926], respectively). The prevalence of CRC was not significantly different between men and women (0.57% [201/35,226] vs. 0.62% [112/17,926], P = 0.440).

Histological findings

The histological analysis indicated that 5.41% of individuals (2873) had hyperplastic polyps (men vs. women, 2250/35,226 [6.39%] vs. 623/17,926 [3.48%], P < 0.001), while 14.58% (7750) had adenomas (men vs. women, 6058 [17.20%] vs. 1692 [9.44%], P < 0.001). Another 0.30% (159) had high-grade intraepithelial neoplasia (men vs. women, 120 [0.34%] vs. 39 [0.22%], P = 0.014); 0.59% (313) had CRC (men vs. women, 201 [0.57%] vs. 112 [0.62%], P = 0.440); 1.23% (653) had serrated adenomas (men vs. women, 548 [1.56%] vs. 105 [0.59%], P < 0.001); and 8.24% (4382) had other benign lesions [Table 2]. In addition, of the 14.58% (95% CI, 14.21–14.81%, 7750) of adenomas, 3.09% (95% CI, 2.90–3.19%, 1641) were classified as AAs.

Table 2 - Detection rates and NNS of adenomas, AAs, CRCs and serrated adenomas in different gender groups receiving colonscopic screening (35,226 of men and 17,926 of women).
Detection rate NNS (95% CI)


Items Men ( n [%]) Women ( n [%]) Men Women χ 2 P values
Adenomas 5.83 (5.70–5.97) 10.68 (10.21–11.19) 414.98 <0.001
 Negative 29,168 (82.80) 16,234 (90.56)
 Positive 6058 (17.20) 1692 (9.44)
AAs 27.25 (25.84–28.82) 55.25 (50.00–61.11) 137.95 <0.001
 Negative 33,917 (96.28) 17,594 (98.15)
 Positive 1309 (3.72) 332 (1.85)
CRCs 175.44 (153.85–204.08) 161.29 (135.14–196.08) 0.60 0.440
 Negative 35,025 (99.43) 17,814 (99.38)
 Positive 201 (0.57) 112 (0.62)
Serrated adenomas 64.10 (59.17–69.93) 169.49 (142.86–212.77) 92.10 <0.001
 Negative 34,678 (98.44) 17,821 (99.41)
 Positive 548 (1.56) 105 (0.59)
AAs, Advanced adenomas; CI, Confidence interval; CRCs, Colorectal cancers; NNS, Number needed to screen; –, Not applicable.

Detection rates for CRCs, AAs, adenomas, and serrated adenomas

Overall, the detection rates for CRCs, AAs, adenomas, and serrated adenomas were 0.59% (313), 3.09% (1641), 14.58% (7750), and 1.23% (653), respectively. Furthermore, we calculated that the number of colonoscopies to detect each one of CRC, AA, adenoma, and serrated adenoma was 169, 33, 7, and 81, respectively.

According to Figure 1, the detection rates of adenomas, AAs, CRCs, and serrated adenomas increased with age and were mostly higher among men. For example, the detection rate of AAs among men aged 60 to 64 years was 6.35% (144/2268, 95% CI 5.35–7.35%) which was significantly higher than that among women of the same age range (42/1592, 2.64%, 95% CI 1.85–3.43%) [Supplementary Table 1, https://links.lww.com/CM9/B277].

F1
Figure 1:
Colonoscopy detection rates of adenomas (A), AAs (B), CRCs (C) and serrated adenomas (D) in different age groups of men and women of the enrolled 53,152 individuals. AAs: Advanced adenomas; CRCs: Colorectal cancers.

Figure 2 showed the anatomical location distribution of advanced colorectal adenoma. Regarding to the anatomical location of CRCs and AAs, more neoplasms were identified in the distal colon than in the proximal colon. Among them, 78.8% of CRCs, 64.2% of AAs, and 66.4% of AAs >1 cm were located in the distal colon.

F2
Figure 2:
Anatomical location distribution of CRCs, AAs and serrated adenomas of the enrolled 53,152 individuals based on colonoscopy. AAs: advanced adenomas; CRCs: Colorectal cancers.

Detection rate and NNS for adenomas

The detection rate of adenomas was 17.20% (95% CI 16.74–17.53) for men and 9.44% (95% CI 8.94–9.79) for women (P < 0.001) [Table 2]. The detection rate of adenomas among men aged 45 to 49 years old was 16.11% (1371/8510, 95% CI 15.28–16.84%), which was higher than that among women in the same age group (7.92% [324/4091, 95% CI 6.95–8.59%]). The detection rate among men aged 50 to 54 years old was greater than that among women of the same age group (19.76% [1669/8447], 95% CI 18.91–20.61% vs. 9.47% [415/4383], 95% CI 8.60–10.33%) [Supplementary Table 1, https://links.lww.com/CM9/B277].

The mean NNS for adenomas was 6.89 (95% CI 6.75–7.04) for all individuals, to be specific, 5.83 (95% CI 5.70–5.97) for men, and 10.68 for women (95% CI 10.21–11.19). In the age group of 45 to 49 years, NNS of women was nearly twice as high as that of men (12.87 [95% CI 11.64–14.39] vs. 6.23 [95% CI 5.94–6.54]).

Detection rate and NNS for AAs

As shown in Table 2, the detection rate of AAs in men was higher than that in women (3.72% [1309/35,226], 95% CI 3.47–3.87% vs. 1.85% [332/17,926], 95% CI 1.61–2.00%, P < 0.001). In the age group of 45 to 49 years, men had 3.17% [270/8510], 95% CI 2.80–3.55% of the detection rate, which was about twice as high as that of women (1.69% [69/4091], 95% CI 1.12–1.86%, P < 0.001). The detection rate of men aged 50 to 54 years was also more than twice that of women in the same age group (4.31% [364/8447], 95% CI 3.88–4.74% vs. 1.69% [74/4383], 95% CI 1.31–2.07%) [Supplementary Table 1, https://links.lww.com/CM9/B277].

The NNS for AAs was 32.89 (95% CI 31.35–34.48) for all individuals, 55.25 (95% CI 50.00–61.11) for women, and 27.25 (95% CI 25.84–28.82) for men [Table 2]. Among 45 to 49-year-old women, the NNS for AAs was 67.11 (95% CI 53.76–89.29) and that of men in the same group was 31.55 (95% CI 28.17–35.71) [Supplementary Table 1, https://links.lww.com/CM9/B277].

Detection rate and NNS for CRCs

Men had a similar detection rate of CRCs compared with women (0.57% [95% CI 0.49–0.65%] vs. 0.62% [95% CI 0.51–0.74%], P = 0.440) [Table 2]. The detection rate among 60 to 64-year-old men (1.76% [40/2268], 95% CI 1.22–2.31%) was slightly higher than that of women in the same age group (1.07% [17/1592], 95% CI 0.56–1.57%) [Supplementary Table 1, https://links.lww.com/CM9/B277].

The mean NNS for CRCs was 169.49 (95% CI 153.85–192.31) for all individuals, 175.44 (95% CI 153.85–204.08) for men and 161.29 (95% CI 135.14–196.08) for women. The NNS for CRCs in men aged 60 to 64 years was lower than that in women of the same age (56.82 [95% CI 43.29–81.97] vs. 93.46 [95% CI 63.69–178.57]).

Detection rate and NNS for serrated adenomas

The detection rate of serrated adenomas in men was more than twice as high as that in women (1.56% [95% CI 1.43–1.69%] vs. 0.59% [95% CI 0.47–0.70%], P < 0.001) [Table 2]. Men had a significantly higher risk of presenting serrated adenomas than women. Similarly, the detection rate of serrated adenomas in men of 45 to 49 years old was more than twice as high as that among women in the same age group (1.39% [118/8510], 95% CI 1.14–1.64% vs. 0.51% [21/4091], 95% CI 0.29–0.73%, P < 0.001). The detection rate of serrated adenomas in men aged 50 to 54 years was three times higher than that in women of the same age group (1.66% [140/8447], 95% CI 1.39–1.93% and 0.55% [24/4383], 95% CI 0.33–0.77%, P < 0.001, respectively) [Supplementary Table 2, https://links.lww.com/CM9/B277].

The NNS for a serrated adenoma was 81.30 (95% CI 75.76–99.01) for all individuals, 64.10 (95% CI 59.17–69.93) for men and 169.49 (95% CI 142.86–212.77) for women [Table 2]. For women aged 45 to 49 years, the NNS was 196.08 (95% CI 136.99–344.83), while men of the same group had the NNS of 71.94 (95% CI 60.98–87.72). Men aged 50 to 54 years had a lower NNS than women of the same age group (60.24 [95% CI 51.81–71.94] vs. 185.19 [95% CI 129.87–303.03]) [Supplementary Table 2, https://links.lww.com/CM9/B277].

Discussion

We reported the results of 53,152 participants who underwent CRC opportunistic screening in an average-risk population from China. The results showed that the detection rates of adenomas, AAs, serrated adenomas, and CRCs were 14.58% (7750), 3.09% (1641), 1.23% (653), and 0.59% (313), respectively. Those of adenomas, AAs, and serrated adenomas increased with age and were higher in men. The majority of AAs was found in the distal colon. The detection rates of AAs in men aged 45 to 49 years were about twice of those of women in the same age group (P < 0.001), and the NNS for AAs was 31.55 (95% CI 28.17–35.71) among men aged 45 to 49 years and 67.11 (95% CI 53.76–89.29) among women of the same age group. Our study enrolled a large population to present the detection rates and the NNS for adenomas, AAs, and CRCs in the asymptomatic average risk population in China.

Effective colonoscopy is necessary for the early diagnosis of CRC precursor lesions, adenomas, or serrated lesions. The ADR, which is correlated with the polyp detection rate and the mean number of adenomas per colonoscopy, has been confirmed by endoscopic physicians to be a predictor of the quality of colonoscopy.[10] Simultaneously, the detection rate of serrated lesions is an important index of colonoscopy quality.[11] In previous studies, the detection rate of adenomas by endoscopists varied greatly,[16,17] and the Colorectal Cancer Screening for Average-Risk Adults: 2018 Guideline from the American Gastroenterological Society and the American Society of Gastrointestinal Endoscopy suggested that the target ADR should be >25% among the population aged 50 years or older undergoing screening colonoscopy.[18] Notably, however, the definition of this target rate is based primarily on evidence from Western populations, which generally have a higher prevalence of CRC. For example, in a screening cohort of 9989 colonoscopies in the United States, the total ADR was 37.2%,[19] and in another opportunistic screening cohort of 4,407,971 colonoscopies in Germany from 2003 to 2012, the ADR of men and women in 2012 was 31.3% and 20.1%, respectively.[20] A recent study from a Chinese population showed that the total ADR of adenomas in a high-risk population was 11.49%,[15] and another study suggested that the detection rate of AAs was 1.27%.[21] The detection rate of colorectal adenomas in our study was lower than that in the above reports, possibly because the incidence of CRC in China was lower than that in European and North American countries.[22] In addition, as this cohort is the population who underwent health physical examinations, rather than involving the high-risk or clinical population, the detection rate might be lower.

The colonoscope reaching the cecum, documented by a picture of the ileocecal valve, was defined as a complete colonoscopic examination, which was >98%. The withdrawal duration of the colonoscopy procedure was at least 6 min to minimize the chance of missing lesions. As the expert opinion suggests, the “mean withdrawal duration should be >6 min in colonoscopies with normal results performed in individuals with intact colons”.[23] The diagnostic accuracy of colonoscopy depends on the cleanliness of the colon and the ability to find lesions. Poor preparation leads to not only missed lesions but also a prolonged duration of the procedure, repeated exams at earlier intervals, increased complications, and excessive costs. The Boston Bowel Preparation Scale that we used has been shown to be reliable.[24] Colonoscopy quality metrics meet the relevant national standards and requirements.

A recent study from France showed that the detection rate of adenomas and AAs increased starting from the age of 45 years, and no significant increase in ADR and advanced neoplasia detection rates (ANDR) was observed between patients aged 45 to 49 years and those aged 50 to 54 years in a screening cohort with 6027 participants undergoing screening colonoscopies.[25] The study from the New Hampshire Colonoscopy Registry suggested that the prevalence of both advanced neoplasia (AN) and clinically significant serrated polyps was similar in the age groups of 45 to 49 and 50 to 54 years.[26] In another study using 6680 colonoscopy screening records from Korea, there was a significantly greater prevalence of adenomas and AAs in individuals aged 50 to 59 years (n = 4474) than those aged 40 to 49 years (n = 2206, 26.7% and 2.4% vs. 37.8% and 3.5%, respectively).[27] Our study indicated that the ADR and ANDR among 50 to 54 year-old individuals were 16.24% (2084/12,830) and 3.41%(438/12,830), respectively, which were greater than the detection rate among individuals aged 45 to 49 years (13.45%, 1695/12,601 and 2.69%, 339/12,601, respectively). Our data were consistent with the above report from Korea[27].

The detection rate of adenomas increased in women aged 55 to 64 years (from 12.01%, 300/2498 of those aged 55–59 years to 14.32%, 228/1592 of 60–64 years), and a similar increase was observed in men 15 years younger, that is, men aged 40 to 49 years, from 12.22% to 16.11%, consistent with the research results of Ferlitsch et al[14]. The detection rate of AAs in women aged 60 to 69 years increased (from 2.64%, 42/1592 to 3.44%, 26/755), which was similar to the prevalence of AAs in men aged 45 to 49 years (3.17%). The detection rate of CRCs was similar between men and women aged 60 to 64 years (1.76%, 40/2268 vs. 1.07%, 17/1592) and higher than that in men (0.73%, 33/4519) and women (0.64%, 16/2498) aged 55 to 59 years. It takes approximately 10 years from the first abnormality to a possible malignancy. The increase in the number of CRCs diagnosed between the ages of 60 to 64 years may reflect a shift from adenomas that were presented in individuals in their 50s.

In our study, the NNS of adenomas and AAs for men aged 50 to 54 years was 5.06 (95% CI 4.85–5.29) and 23.20 (95% CI 21.10–25.77), while the NNS was 10.56 (95% CI 9.68–11.63) and 59.17 (95% CI 48.31–76.34) for women in the same age group. It is important to begin CRC screening in men under the age of 50 years to avoid the high prevalence. Because advanced neoplasms are more common in the distal colon, complete colonoscopy plays an important role as a screening tool to detect and remove all adenomas and AAs.[28] The number of colonoscopies to detect each one of CRC, AA, and adenoma was 169, 33, and 7, respectively, so further efforts to optimize the screening strategy by incorporating risk score and non-invasive tests (such as FOBT) are highly required for people under the age of 45 years.[29]

A major advantage of the study is that it enrolled a large average-risk population-based cohort in China to demonstrate the detection rate of screening colonoscopy, and the large amount of data from younger individuals allows the analysis on the prevalence of adenoma, AAs, and CRC. In addition, detailed clinical examination data (colonoscopy and pathology) were collected in a standardized model by trained researchers to ensure the quality of the data. Another advantage is that all colonoscopies were subject to the same quality control, thus providing comparable data for adenomas, AAs, and CRCs.

One limitation of this study is that it was a single-center study and could not completely represent the general population of China, so selection bias cannot be ruled out. Second, the study mainly aimed to determine the detection rates of adenomas and AAs, so the impact of lifestyle on adenomas and AAs can be studied in the future.

In summary, in this large-scale CRC opportunistic screening study in China, we found that the detection rate of adenomas, AAs, and serrated adenomas is high in the asymptomatic population undergoing a physical examination and is associated with gender and age. Further efforts to optimize the screening strategy by risk score and non-invasive tests (such as FOBT) are highly needed. These findings provide clues for effective population-based CRC screening strategies in China.

Funding

This work was supported by the State Science and Technology Support Program (No. 2012BAI37B04) and the Joint Project of the National Natural Science Foundation of China and the Australian National Health and Medical Research Council (No. NSFC81561128020-NHMRCAPP1112767).

Conflicts of interests

None.

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Keywords:

Adenomas; Advanced adenomas; Colorectal cancer; Gender disparity; Opportunistic colonoscopy screening

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