Colonoscopy: is it as effective as an advanced diagnostic tool for colorectal cancer screening?

Abstract

A broad range of modalities for colorectal cancer (CRC) screening are available worldwide. Although recent studies have been demonstrating developments of CRC screening modalities including colonoscopy, computed tomography colonography or colon video capsule colonoscopy remains the gold standard for the early detection of adenoma or CRC. Because patient preferences and availability of resources play an important role in the selection of CRC screening options, further improvement of each screening modality and its associated research is necessary to consider its involvement in clinical practice.

Keywords:

• adenoma detection rate
• colonic polyps
• colonoscope
• colorectal cancer screening

Colorectal cancer (CRC) is the third most common cancer worldwide and the fourth most common cause of death [1]. Because the most important clinical outcome in patients at risk for CRC is identification and treatment at the earlier clinicopathological stage, the primary goal of CRC screening should be early detection of precursor lesions. In fact, the 5-year relative survival rate with CRC identified and treated in stage I has been shown to be greater than 90% [2].

A broad range of screening modalities for CRC are available. These include stool-based studies such as fecal occult blood test and stool DNA tests, barium enema, colon video capsule, colonoscopy and computed tomography colonography. Although recent studies have been demonstrating new developments and improvements in CRC screening, colonoscopy is still regarded as the gold standard screening modality despite recent reports showing comparable results with some other specific modalities [3–5].

The evolution of these new modalities provokes discussion and begs the question ‘Is colonoscopy as effective as an advanced diagnostic tool for CRC screening?’ We would like to address this question and focus on colonoscopy as a current clinical application for screening and diagnosis of CRC.

Advantages of colonoscopy in CRC screening & surveillance

Because colonoscopy has the ability to inspect the entire colorectal mucosa and can detect even small, diminutive or flat lesions, it is the most widely acceptable modality for CRC screening and surveillance. In addition, one of the important advantages of colonoscopy is the ability to perform biopsy, polypectomy and endoscopic mucosal resection for adenomas and early-stage cancers at the same time. The National Polyp Study cohort reported that colonoscopic polypectomy for adenomatous lesions reduced the incidence of CRC by 76–90% based on the evidence of an adenoma–carcinoma sequence [6]. Furthermore, a long-term follow-up study of the National Polyp Study cohort demonstrated that polypectomy resulted in reduced mortality from CRC [7].

Improvement of adenoma detection rates

Although colonoscopy has been considered as the gold standard examination for the detection of colorectal lesions, miss rates for adenomas less than 1 cm in diameter of up to 15–27% have been reported using a standard colonoscopy [8,9]. In addition, the adenoma detection rate (ADR) of the endoscopist is inversely correlated with the subsequent rate of interval CRCs [10]. Corley et al. also demonstrated that physicians’ ADR and the risk of interval CRCs including advanced-stage cancer was not perfectly linear using the database of the US integrated health care delivery organization [11]. So, further studies to determine whether improving the ADR leads to improved outcomes are warranted. Improvement of the ADR, however, is required for adequate screening and surveillance colonoscopy. In the following paragraph, we would like to discuss high-quality withdrawal techniques and the efficacy of some novel technologies.

Colonoscope with multiple views

A major contributing factor of missed lesions may be those undetected that are located behind haustral folds, flexures, ileocecal valves or rectal valves. To improve the ADR, various techniques and technologies including the use of a distal attachment on the tip of a colonoscope called cap-assisted colonoscopy, observation under retroflexion of the colonoscope and the use of wide-angle colonoscopy have been assessed in many studies with mixed results. Some are controversial and some report improvement in the ADR [12–14].

A retrograde viewing auxiliary imaging device, Third Eye Retroscope (Avantis Medical Systems, Inc., Sunnyvale, CA, USA), has been developed [15]. This unique device can be passed through the working channel of a standard colonoscope providing a retrograde view of the colon during withdrawal, enabling the detection of polyps located behind haustral folds and flexures. Several multicenter prospective clinical studies revealed that this device increased the ADR. In addition, the Fuse Full Spectrum Endoscopy System (EndoChoice, Alpharetta, GA, USA) has been developed and most recently became available [16]. This has three charge-coupled device lenses at the tip of the endoscope and two lateral lenses that provide a retrograde view of the colon during withdrawal, enabling the detection of hidden polyps. Recent multicenter clinical trials revealed that the use of this novel colonoscope increased the ADR. Despite these advantages of the Third Eye Retroscope and the unique Fuse Full Spectrum Endoscopy System, both have several limitations. Firstly, the Third Eye Retroscope requires two endoscopy system units including a split-screen and two video displays for the forward and retrograde views. The Fuse Full Spectrum Endoscopy System also needs a split-screen and three video displays for the central, right and left side views. With these multiple screen views, endoscopists might have to expand their visual focus to avoid missing lesions on the multiple video displays. In addition, the Third Eye Retroscope is also a disposable device with a relatively high cost (US$350 for the disposable catheter). Finally, it does increase the procedure time if therapy is required due to any intervention and complication.

Presently, we are evaluating the extra-wide-angle-view colonoscope (Olympus Co., Tokyo, Japan) [17]. The prototype of the extra-wide-angle view colonoscope (Olympus Co., Tokyo, Japan) has two lenses, a 144°-to-232°-angle lateral-backward view lens and a standard 140°-angle forward view lens. The lateral-backward view lens is projected in a convex shape from the tip of the colonoscope. Views from both lenses are simultaneously displayed on a video monitor as a single image. In our simulated pilot study using anatomical colorectal models, we have clearly demonstrated the significantly higher detection rate of simulated polyps in obvious locations in a novel prototype of the extra-wide-angle-view colonoscope than the standard colonoscope groups (68 vs 51%; p < 0.0001). The detection rate for polyps behind folds was also significantly higher with this novel colonoscope than with the standard colonoscope (61.7 vs 46.9%; p = 0.0009). The novel extra-wide-angle-view colonoscope may represent advancement in colorectal polyp detection. Therefore, further evaluation involving a randomized controlled multicenter trial should be seriously considered to fully evaluate the efficacy for screening and surveillance of CRC.

Narrow band imaging

Narrow band imaging (NBI) relies on the light absorption properties of hemoglobin. A rotating optical filter located behind the light source of the colonoscope is manually activated by a switch allowing ambient light of 440–460 nm (blue) and 540–560 nm (green) to reach the mucosa. Based on this modification, NBI enhances mucosal visualization of the vascular network and surface structure by improving contrast, which helps to increase the visibility of neoplasia [18]. Many studies have investigated the comparison of detection of adenoma using NBI and white light imaging; however, recent meta-analyses of comparative outcome studies demonstrated that NBI negatively affects ADRs [19]. The main reason considered for the negative results was the limitations of NBI image brightness. However, this brightness has been improved in the second generation of NBI-based Olympus 190 system, which is now widely available. The most recent randomized controlled study found that using the NBI system 190, there was significantly higher ADRs compared to high-definition white light image [20].

Capsule endoscopy for CRC screening

Colon capsule endoscopy (CCE) was first reported in 2006 [21]. To assess the detection of colorectal neoplasia, Van Gossum et al. [4] conducted a large-scale clinical trial. They reported that the sensitivity and specificity of CCE for detecting polyps that were 6 mm in size or bigger were 64 and 84%, respectively. They concluded that first-generation CCE has only moderate sensitivity and specificity as compared with conventional colonoscopy for colon polyp surveillance. To resolve this inferiority to colonoscopy, second-generation CCE (CCE-2) has been developed [22]. The CCE-2 device is equipped with a high frame rate camera, which can take 4–35 pictures per second when the capsule is accelerated by peristalsis. Spada et al. [23] conducted a multicenter study by using CCE-2. They concluded that CCE-2 has high sensitivity for the detection of clinically relevant polypoid lesions. Furthermore, standard CCE preparation consists of 4–6 l of PEG and sodium phosphate solution as boosters, and preparation needs to be started a few days before the examination. These multistep preparations need to be simplified to improve patients’ acceptance. One of the most important factors is the volume of laxatives and this should hopefully be reduced in the near future. One of the disadvantages of CCE is that same-session biopsy, polypectomy and endoscopic mucosal resection cannot be performed even with early detection of adenomas and early-stage cancers. However, CCE has been accepted as a screening modality in the western countries.

Conclusion

While various imaging modalities have been attempted in CRC screening in recent years, the image quality of colonoscopy has been improved to facilitate improved ADR. In addition, colonoscopy can evaluate the lesion characteristics including differentiating between adenoma or hyperplastic polyp or staging of precancerous lesion or early-stage cancer. Moreover, colonoscopy has the added advantage of simultaneously facilitating therapeutic interventions such as biopsies, polypectomy or removing early-stage cancer, resulting in long-term prevention of CRC-related deaths. Earlier in the introduction we asked ourselves ‘Is colonoscopy as effective as an advanced diagnostic tool for CRC screening?’ We believe the answer to this question is a resounding ‘yes.’ Colonoscopy remains the gold standard modality for the early detection of adenoma or CRC. Because patient preferences and availability of resources play an important role in the selection of CRC screening options, further improvement of each screening colonoscopy modality and research should be considered in clinical practice.

Acknowledgements

The authors express their appreciation to H Ramberan for his assistance in editing this manuscript.

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.