The Prevalence of Post-colonoscopy Colorectal Cancers Using the World Endoscopy Organization Nomenclature

Abstract and Introduction

Abstract

Introduction: Post-colonoscopy colorectal cancers (PCCRCs) have been proposed as a performance metric for colonoscopy quality assurance programs. Previously, there was no standardised terminology or reporting methods. In 2018, the World Endoscopy Organization (WEO) advised standardised definitions and prevalence calculation methodology.

Aims: To assess PCCRC burden using WEO standardised methods, to explore causes of heterogeneity, and to review changes in prevalence over time

Methods: We updated a prior systematic review by searching Ovid MEDLINE and EMBASE databases from 1 January 2013 to 31 January 2021 to identify population-based studies (or multicentre studies representative of the local population) reporting PCCRC prevalence (PROSPERO [CRD42020183796]). Two authors independently determined study eligibility, assessed quality, and extracted data. We estimated the PCCRC 3-year prevalence using WEO-recommended methodologies and investigated between-study sources of heterogeneity. We examined changes in prevalence over time.

Results: Fifteen studies reporting on 25 872 PCCRC cases met eligibility criteria. Pooled PCCRC 3 year prevalence was 8.2% (95% CI = 6.9%-9.4%, I ² = 98.2%) across four European studies using WEO precise methodology. Proximal PCCRC prevalence was greater than distal (9.7% [95% CI = 7.0%-12.4%] vs 5.4% [95% CI = 2.9%-7.8%], I ² = 99.2%). Seven studies reporting PCCRC rates over time showed no consistent trend: four showed a decrease, one an increase and two were unchanged. Between-study heterogeneity was high.

Conclusions: Pooled 3-year PCCRC prevalence was 8.2% (95% CI = 6.9%-9.4%). Despite WEO standardised methodology to define and calculate PCCRC rates, there was significant heterogeneity among studies. Comparing rates between populations remains challenging and additional studies are needed to better understand the global PCCRC burden to inform quality assurance programs.

Introduction

Colorectal cancer (CRC) is the third commonest malignancy and fourth leading cause of cancer deaths globally.^[1] It is predicted that there will be more than 2.2 million new cases and 1.1 million cancer deaths by 2030.^[2] Survival is strongly related to stage at diagnosis.^[3] Population-based screening and surveillance with colonoscopic removal of premalignant lesions significantly reduces CRC incidence and mortality.^[4]

The United States Preventive Services Task Force consensus guideline 2020 recommends risk stratification post-polypectomy surveillance according to the number and size of resected polyps: 7–10 years for low-risk, 3–5 years for intermediate-risk and 1 year for high-risk patients.^[5] UK guidance from 2020 advises repeat colonoscopic surveillance following adenoma removal at 3 years for high-risk patients, and for lower-risk patients either at 5–10 years or not at all.^[6]

However, despite these guidelines, some patients develop CRC after a clearing colonoscopy in which no cancer is diagnosed^[7] and before the next surveillance colonoscopy after the recommended interval. Possible reasons for such “post-colonoscopy” CRCs (PCCRCs) include: incomplete colonoscopy, missed lesions, incomplete polypectomy, rapidly growing lesions and iatrogenic seeding of cancer via the biopsy channel of the colonoscope.^[8] The importance of procedural and patient-related risk factors was emphasised in a UK-based series of 107 PCCRC patients, in which inadequate previous colonoscopy was implicated in 58% cases while 43% PCCRCs occurred in patients with high-risk comorbidities.^[9] Biological differences have also been demonstrated in cohort studies between the cancers of PCCRC patients compared with detected CRC.^[10–12]

Until recently, the terms “interval,” and PCCRCs were used interchangeably, with rates shown to vary considerably, ranging from 2.5% to 7.7%, depending on the method used for their calculation.^[13] A standardised definition and methodology for determining PCCRC prevalence is therefore necessary to enable more direct comparisons between services. A recent World Endoscopy Organization (WEO) consensus statement recommended the term PCCRC to define CRCs appearing after a colonoscopy in which no cancer is diagnosed and its use as a clinically relevant quality metric.^[14] Clearly the number of PCCRCs will increase commensurate with the time period of observation following index colonoscopy. The WEO recommended that, as a minimum, PCCRC rate should be reported for an interval of 6–36 months after an index colonoscopy negative for cancer to enable benchmarking between services.^[14]

PCCRCs comprise both “interval” and “non-interval” cancers following colonoscopy. Interval CRCs occur in the context of screening and surveillance when a CRC is identified before the next recommended examination. Non-interval PCCRCs occur when a CRC is identified either at or after a recommended screening or surveillance colonoscopy, or following an examination for which no repeat was recommended, up to 10 years after the colonoscopy.^[14]

The objective of this study was to establish the global burden of PCCRC, following on from previously reported pooled prevalence estimates by Singh et al^[15] using studies which follow the newly standardised WEO-endorsed terminology for PCCRCs. In addition, we explore potential causes of heterogeneity in pooled PCCRC prevalence estimates and examine changes in PCCRC prevalence over time.