Colorectal polyp prevalence and adenoma detection rates in an Iranian cohort: a prospective study

Abstract

Background

Colorectal cancer (CRC) prevention relies on early diagnosis and endoscopic resection of adenomatous polyps. This in turn depends on the quality of the performed colonoscopy. “Polyp detection rate, PDR” and “adenoma detection rate, ADR” are considered indices for quality of colonoscopy. This study aims to evaluate PDR and ADR, alongside the demographic, clinical, and pathological characteristics of colorectal polyps in an Iranian population. We also aimed to find the prevalence of colon polyps among different age groups.

Methods

All consenting patients 40 years of age or older undergoing screening colonoscopy or for possible IBS in a referral center in Tehran over 10 years were enrolled. We collected demographic data, quality of colon preparation, time to cecum, withdrawal time and colonoscopic findings. PDR and ADR were calculated and correlated with the above-mentioned indices.

Results

A total of 3,416 (mean age 57.6 ± 9.8 years) people meeting the inclusion criteria were enrolled. Successful ileal intubation occurred in 54.6%. PDR was 41.5% (95% CI: 39.9–43.3%) being higher in men (46.8% vs. 36.9%; p = 0.01). Individuals aged 45–49 years exhibited a greater likelihood of colorectal polyps than younger counterparts (34.2% vs. 21.9%, p = 0.001). Overall ADR was 26.4% (95% CI: 25.01-27.9%), with patients older than 50 years having a higher rate (29.3% vs. 16.3%).

Conclusion

Our data shows acceptable PDR and ADR in this referral center and higher prevalence of adenomatous polyps in men in accordance with western reports. In addition, according to our data substantial proportion of individuals aged 45–49 years were found to harbor adenomatous polyps, aligning with trends observed in Western populations. If further research confirms these findings, it could provide a rationale for considering the initiation of colorectal cancer screening at age 45 in Iran.

Introduction

Colorectal Cancer (CRC) is a major global health burden, by being the third most prevalent cancer in men and the second in women [1]. It accounts for 10% of all cancer cases, with 1.9 million new diagnoses and 0.94 million deaths in 2020 globally [2]. By 2040, the annual incidence is projected to rise to 3.2 million [3]. Recent advancements in treatment options, including surgical excision, radiotherapy, immunotherapy, and chemotherapy have improved survival rates [4, 5]. CRC develops slowly from precancerous lesions to invasive cancer, therefore, early detection and removal of these pre-cancerous lesions are crucial to reduce incidence and mortality [3]. Among all the screening methods, colonoscopy stands out as the most effective one and is widely adopted across various economic contexts [6, 7]. Quality of the performed colonoscopies is pivotal for the screening to be effective [8]. Almost all of CRC cases arise from adenomas in the colon, making high-quality colonoscopy screening with an acceptable adenoma detection rate (ADR), a preferred method for CRC prevention [9, 10].

As CRC is getting more prevalent with increasing age, screening is recommended from age 50. However, recent data indicate that 11% of CRC cases in men and 10% in women occur before age 50, prompting a reevaluation of the screening age [11, 12]. Recent studies suggest that the Age-Standardized Incidence Rate (ASR) for younger populations in Iran and the U.S. is similar [13], with a significant number of colorectal cancer (CRC) cases being diagnosed in individuals under the age of 50 [14].

The rising CRC incidence, particularly among younger populations, can have a significant impact on society [15–17]. In response to the rising CRC incidence, particularly among younger people, some Western guidelines have lowered the screening age to 45 [18, 19].

Iran is witnessing a similar increase in CRC cases. The incidence rate increased significantly from 6.4 in 2003 to 9.3 cases per 100,000 persons in 2010 [20]. The estimated incidence rate for 2025 is 17.7 per 100,000 persons, with more than 17,800 patients [14]. Our study aims to estimate the polyp detection rate (PDR) and ADR as indices of quality of the colonoscopies performed as well as comparing the frequency of polyps in individuals under 50 years old with those aged 50 and above.

Methods

Patients, procedures, and measures

All 40 years and older patients scheduled for screening colonoscopy, or undergoing colonoscopy for irritable bowel syndrome (IBS) type symptoms in a referral clinic in Tehran between 2012 and 2022 were invited to participate in the study. Exclusion criteria were prior colonoscopies, personal history of colon cancer or polyps, previous colon surgery, and colorectal conditions such as inflammatory bowel disease (IBD), hematochezia, positive stool occult blood test, or iron deficiency anemia. Expert gastroenterologists performed the procedures under anesthesia.

Patient demographics, colonoscopy indications, quality of bowel preparation, and procedure duration were documented. Bowel preparation was assessed by the “Boston Bowel Preparation Scale” that scores from 0 to 9 [21]. A score of 9 was considered as excellent, 6,7 and 8 as acceptable, 4 and 5 as poor and 3 or lower as very poor. Procedure times (insertion and withdrawal) were measured with a chronometer, excluding polyp removal duration. Clinical and pathological data on colorectal lesions, including number, size, location, and histopathologic characteristics of polyps, were recorded. Pathological assessments were conducted by two experienced GI pathologists. Adenomas were defined as polyps exhibiting tubular, tubulovillous, villous, or sessile serrated features.

PDR was calculated as the ratio of procedures detecting at least one polyp to the total number of colonoscopies. Similarly, ADR was determined as the ratio of procedures identifying at least one adenoma. Colonic segments were categorized as right (transverse colon, hepatic flexure, ascending colon, and cecum) or left (rectum, sigmoid, descending colon, and splenic flexure). Polyp sizes were compared and classified as < 10 mm or ≥ 10 mm in diameter. Three age groups were compared, 40–44 years, 45–49 years, and ≥ 50 years. Details of the study and use of data were explained to all participants and a written informed consent was obtained from all participants, and the ethics committee of Tehran University of Medical Sciences approved the study. (Ethical number: IR.TUMS.MEDICINE.REC.1395.1820)

Statistical analysis

Categorical variables were described using frequencies and percentages, while continuous variables were summarized using means and standard deviations. The Chi-square test was used for categorical data comparison across subgroups. The Benjamini-Hochberg procedure was performed to adjust p-values when comparing subgroups. A p-value of 0.05 or less was set for statistical significance. All analyses were conducted using Stata version 16. (StataCorp. 2019. Stata Statistical Software: Release 16. College Station, TX: StataCorp LLC.)

Results

Patient demographics

Overall, 3,416 individuals were enrolled, 2,647 of whom were 50 years and older. The mean age was 57.6 years (± 9.8), and 1,576 (46.1%) were male. One-hundred and twenty-nine participants underwent colonoscopy due to IBS symptoms, while the rest were completely asymptomatic.

Bowel Preparation and procedure details

The quality of Bowel preparation varied among participants, with 19 rated as very poor, 251 poor, 2196 acceptable, and 821 excellent. Ileal intubation was done in 1,726 patients (Table 1). The mean time to reach the cecum was 362 s (± 224s) and the mean withdrawal time was 557 s (± 382s). The average procedure time was 919 s (± 445s).

Table 1.

Patients’ characteristics and colonoscopy findings

Variable	N = 3416
Age, mean years (SD)	57.66 (± 9.81)
Sex, Male/Female, n (%)	1576 (46.1%)/1840 (53.9%)
Preparation quality, n (%) Very poor/poor Acceptable Excellent	270 (7.9%)
	2196 (64.3%)
	821 (24.0%)
Ileal intubation, n (%) Yes No	1726 (50.5%)
	1690 (49.5%)
Patients with at least 1 polyp, n (%)	1420 (41.5%)
Patients with at least 1 adenoma, n (%)	903 (26.4%)
Patients with cancerous lesion, n (%)	7 (0.2%)

Polyp characteristics

A total of 3,180 polyps were identified, in 1420 patients. Tubular adenoma with low-grade dysplasia (n = 1217, 38.2%) and hyperplastic polyps (n = 663, 20.8%) were the most common types. Carcinoma in situ was found in seven patients (0.2%). Among the 3,180 polyps examined, 1,191 were classified as benign lesions, encompassing a variety of histopathological subtypes including hyperplastic polyps, regenerative/reparative polyps, inflammatory polyps, mucosal tags, prolapse-type polyps, solitary rectal polyps, leiomyomas, hamartomatous polyps, and benign lymphoid nodules (Table 2).

Table 2.

Histopathology features of the detected polyps

Polyp Histopathologic type	N	%
Tubular adenoma with low grade dysplasia	1217	38.2
Tubular adenoma with high grade dysplasia	335	10.5
Tobulovillous Adenoma	170	5.3
Villus Adenoma	18	0.56
Sessile serrated Adenoma	31	0.9
Hyperplastic polyp	663	20.8
Regenerative/reparative polyp	9	0.3
Inflammatory polyp	66	2.0
Mucosal tag	410	12.9
Prolapse type polyp	12	0.4
Solitary rectal polyp	4	0.1
Leiomyoma	5	0.1
Endometriosis	1	0.03
Hamartomateus polyp	2	0.06
Benign lymphoid nodule	19	0.6
Neuroendocrine tumor	2	0.06
Carcinoma in situ	7	0.2
Missing	209	6.5

Most of the polyps, 54.3% (n = 1,729), were found in the left colon ( 795 (25%) in the sigmoid). Regarding size, 41.7% (n = 1,328), were diminutive (< 5 mm in diameter), 45.6% (n = 1452) were 5–10 mm and 12.7% (n = 385) of polyps were larger than 10 mm. Most (55.6%, (n = 214)) of the larger polyps (≥ 10 mm) were located in the distal colon (Table 3).

Table 3.

Distribution of polyps by site

Polyp Location*	Rectum	Sigmoid	Descending colon	Transverse colon	Ascending colon	Cecum
N	513 (16.1%)	795 (25%)	421 (13.2%)	566 (17.8%)	521 (16.4%)	361 (11.3%)
Size** ≤10 mm	465 (14.6%)	672 (21.1%)	373 (11.7%)	494 (15.5%)	449 (14.1%)	330 (10.4%)
Size > 10 mm	46 (1.4%)	120 (3.8%)	48 (1.5%)	72 (2.3%)	70 (2.2%)	29 (0.9%)

*Location of 3 polyps are missing

** Size of 12 polyps are missing

Polyp and adenoma detection rate

At least one polyp was detected in 1,420 patients, resulting in a PDR of 41.5% (95% CI 39.9%-43.2%). The PDR was higher in males (46.8%, 95% CI 44.3%-49.2%) compared to females (36.9%, 95% CI 34.7%-39.1%). When stratified by age, the PDRs were 21.9% for ages 40–44, 34.2% for ages 45–49, and 45.1% for those over 50. PDR for the 45–49 age group was higher than for the 40–44 age group (p = 0.001, Table 4). The PDR showed no significant variation with the quality of bowel preparation (p = 0.298). Dividing participants based on withdrawal times of less or more than six minutes, 1100 participants had a withdrawal time of less than six minutes (32.2%) and 2262 (66.2%) had a withdrawal time longer than six minutes. PDR was 15.3% (95% CI: 13.2-17.4%) and 54.3% (95% CI: 52.2-56.3%), (P-value < 0.001), respectively. The polyp detection rate (PDR) and adenoma detection rate (ADR) were significantly higher among individuals with withdrawal times exceeding 6 min, with an odds ratio of 6.11 (95% CI: 5.19–7.23) compared to those with shorter withdrawal times.

Table 4.

PDR and ADR by age-groups

	40–44 Polyp (%)	45–49 Polyp (%)	≥ 50 Polyp (%)
				40–44 vs. 45–49	40–44 vs. ≥ 50	45–49 vs. ≥ 50
N	319	450	2647	---	---	---
N with polyp (PDR)	70 (21.94%)	154 (34.22%)	1196 (45.18%)	P = 0.00001	P = 0.000001	P = 0.00022
N with adenoma (ADR)	40 (12.53%)	86 (19.11%)	777 (29.35%)	P = 0.000012	P = 0.00003	P = 0.00067

N: Number; P: P-values; PDR: Polyp Detection rate; ADR: Adenoma Detection Rate

Adenomas were identified in 903 patients, resulting in an Adenoma Detection Rate (ADR) of 26.4% (95% CI: 25.01-27.9%). The ADR was higher in males at 31.4% (95% CI: 29.1-31.7%) than in females (22.2%, (95% CI: 20.3-24.1%)). The ADRs across the age groups were 12.5% for 40–44, 19.1% for 45–49, and 29.3% for those above 50. For patients under 50, the ADR was 16.3%. The ADR for the 45–49 age group was significantly higher than the 40–44 group and lower than the above 50 group (p = 0.001), as shown in Table 4.

Discussion

We found that PDR and ADR in an Iranian population over 40 years referring to a referral GI clinic were 41.5% and 26.4%, respectively. These results are comparable with European (PDR of 45.8%) and U.S. studies (PDR of 49%, ADR of 31%) [22–24]. A prior Iranian study by Delavari et al. reported similar PDR and ADR (42% and 33%, respectively) [25, 26]. However, another study in Iran estimated a lower PDR and ADR (23.5% and 12.8%, respectively) [27]. We found that male gender was associated with higher risk of developing colorectal polyps (p = 0.01), which is consistent with previous studies [28–30]. A recent systematic review investigating the risk factors for colorectal cancer in Iran has showed that a growing trend toward western style diet including high consumption of red meat and fried food, and low intake of fruits and vegetables, is associated with higher incidence of colorectal cancer [31]. Those with lower rate of physical activity are also more likely to develop colorectal cancer [32].

Furthermore, genetic factors and family history of CRC may affect prevalence of colorectal polyp, and CRC. As colonoscopy is more likely to detect polyps in people with symptoms such as hematochezia or a positive occult blood in stool. We excluded these groups to avoid inflation of PDR and ADR in our study. Hence, to address this, we enrolled only asymptomatic participants, ensuring that the observed PDR and ADR reflect findings in average-risk individuals rather than those seeking medical care due to the above-mentioned symptoms. This approach minimizes the potential for selection bias and enhances the applicability of our results to the general population. Nonetheless, improving screening participation through targeted interventions—such as formal invitations or public awareness campaigns—remains critical for achieving more representative outcomes and broader public health impact [33, 34].

Our data showed a considerable prevalence (19.0%) of adenomatous polyps among people younger than 50 years old. Considering this and the increasing incidence of CRC among younger patients [35, 36], it may be justifiable to recommend lowering the screening age. This needs further assessment through a cost-benefit analysis before being recommended. Currently all people 50 years and older are encouraged to undergo some form of screening for CRC in Iran, either by FIT or colonoscopy, and this is covered by all insurances. Despite this, there is no national program to enforce the policy and screening participation is low. Hassanlouei et al. reported only a 14% participation using fecal immunochemical tests (FIT) [37], compared to 30–67% in other nations [38, 39].

Although the prevalence of polyps and adenomas in patients older than 50 years is higher, we found a considerable number of polyps and adenomas in patients younger than 50 years, in accordance with increasing CRC prevalence in younger age [40]. The observed increase in colorectal cancer (CRC) incidence may be attributed to shifts in lifestyle habits, including dietary patterns, levels of physical activity, obesity, and alcohol consumption. Consequently, it is essential to conduct further research to elucidate the underlying causes and risk factors associated with this trend. Additionally, there is a pressing need for the implementation of effective and well-structured screening programs aimed at facilitating early diagnosis, which could help alleviate the burden of CRC [13, 41]. Considering the ADR of 19% observed in the45–49 years age group, which represents a substantial proportion, it is imperative to conduct a comprehensive cost-benefit analysis to evaluate the feasibility and potential advantages of lowering the colorectal cancer screening threshold. Such an analysis would provide useful insights into the economic and clinical implications of implementing earlier screening interventions [42].

Longer withdrawal times during colonoscopy, especially beyond six minutes, have been linked to increased polyp detection [10, 43]. The mean time of withdrawal in our study, after subtracting the time for polyp removal, was nine minutes and 17 s. Procedures with withdrawal times of six minutes or longer had a PDR more than three times higher than those with shorter times (54.33% vs. 15.36%, (p < 0.001)). Tubular adenomas were the most common histological type in our study consistent with the findings of previous investigations [27, 44]. Over half of the polyps were found in the left colon (n = 1,729), with the transverse colon having the second-highest detection rate (17.4%). These results are in line with the latest findings suggesting an increasing trend of right-sided polyps [45–47].

According to GLOBOCAN reports, the number of new cases and mortality form CRC will be increasing and by 2040 there will be 3.2 million new cases compared to 1.9 million in 2020 and 1.6 million deaths compared to 930,000 in 2020 [48]. The number of new cancer cases in Iran is expected to rise from 112,000 recorded cases in 2016 to an estimated 160,000 by 2025, reflecting a 42.6% increase [41]. A growing concern is the marked increase in colorectal cancer diagnoses among adults under 50 years old over the past two decades [49]. This trend suggests the need for more effective initiation.

Our study’s limitations include a lower representation of participants under 50 and its single-center nature. Expanding data collection to multiple centers across various cities would be beneficial. We also did not collect data on family history of CRC and colorectal polyps. In addition, all colonoscopies were performed by proceduralists with ≥ 10 years of experience. The ADR and PDR might be different with less experience. The other noticeable point is that the pathologists were not blind to the histopathological report of their colleague. Although this might affect the results, but considering that both pathologists were expert GI pathologists and reviewed the samples independently, this has probably minimal effect on the results. We had 6.5% missing data on histopathology of the polyps. This can potentially affect the results, although probably not substantially. There are some data missing regarding the polyp size (n = 12) and polyp location (n = 3). However, given the scale of our study involving over 3,400 participants, it is very unlikely that these number of missing data affect the overall results.

Conclusion

To the best of our knowledge, this study is the largest study in Iran to assess PDR and ADR in asymptomatic individuals that also includes people 40–49 years old. PDR and ADR are comparable to those reported in Western countries, where CRC is more prevalent. Notably, our data suggests a considerable incidence of colorectal polyps within the younger segment of the population. Given these findings, we strongly endorse the implementation of a comprehensive national population-based study to see if the age of CRC screening should be lowered in Iran, as it has been recently advised in newer western guidelines [18, 19]. This then needs to be complemented by a cost-benefit analysis.

Author contributions

SNM and AS conceptualized and organized the study; AHM and MR were responsible for data curation; AHM, SNM, AS wrote the text; AK analyzed the data; and all authors participated in reviewing and approval of the manuscript. All authors agreed to the submitted version.

Funding

The authors would like to express thanks to the National Institute for Medical Research Development (NIMAD), Tehran, Iran, for their financial support. (Grant No. 97140).

Data availability

The raw data associated with the conclusions of this article will be made accessible by the corresponding author, upon request.

Declarations

Ethics

Ethical committee of Tehran University of Medical Sciences approved the study (Ethical number: IR.TUMS.MEDICINE.REC.1395.1820). The patients provided their written informed consent to participate in this study. All research was performed in accordance with the Declaration of Helsinki and informed consent was obtained from all participants. No individual data is reported and all authors are committed to protecting patients’ data recruited in this study.

Consent for publication

Not applicable.

Conflict of interest

The authors assert that the research was steered in the absence of a commercial or financial relationships that could be interpreted as a potential conflict of interest.