Evaluating the Clinical Value of Transparent Cap-Assisted Second Examination of the Sigmoid Colon for Improving Colorectal Adenoma Detection Rates

Colorectal cancer (CRC) is the third most common malignancy worldwide and the second leading cause of cancer-related mortality. In recent years, with the increasing Westernization of diet and lifestyle, the incidence and prevalence of CRC in China have risen rapidly, making CRC one of the most common gastrointestinal malignancies in the country. Its incidence and mortality now rank second and fifth, respectively, among all cancers. The disease burden of CRC in China has become substantial, and reducing its incidence and mortality is an urgent public health priority. Colonoscopy is the gold standard for CRC screening, and timely endoscopic management of precancerous lesions plays a critical role in reducing both CRC incidence and mortality.

Interval CRC refers to cancers diagnosed before the next recommended examination after a negative screening or surveillance colonoscopy. Adenoma detection rate (ADR) is an independent predictor of interval CRC risk; long-term follow-up data suggest that every 1% increase in ADR corresponds to a 5% reduction in the risk of interval CRC and a 3% reduction in mortality. However, emerging evidence indicates that interval CRC can still occur even among endoscopists with high ADRs, suggesting that some precancerous lesions may still be missed.

The main contributors to missed colorectal adenomas include: (1) operator-related factors such as fatigue, reduced attention, or limited lesion recognition; (2) image-related factors such as low-resolution visualization; and (3) inadequate mucosal exposure due to residual folds. In recent years, several studies have explored the use of "repeat intubation" to reduce missed adenomas. Multiple randomized controlled trials (RCTs) and systematic reviews have shown that a second examination can increase ADR, but most studies have focused on the right colon and often relied on chromoendoscopy or other image-enhancement modalities to improve lesion visibility. Evidence regarding second intubation specifically for the sigmoid colon remains limited, and even fewer studies have evaluated interventions based on transparent cap-assisted colonoscopy. Given that the sigmoid colon is a common site for missed polyps and adenomas, optimizing visualization in this segment may have a significant impact on overall ADR and CRC prevention.

In summary, there is still a lack of clinical evidence on whether transparent cap-assisted second intubation of the sigmoid colon can improve colorectal adenoma detection. A randomized controlled trial in the Chinese population is therefore needed to clarify its clinical value, with the potential to increase lesion detection and improve the overall quality of colonoscopy.

Inclusion criteria

• aged 45-75 years

Exclusion criteria

• Patients scheduled for therapeutic colonoscopy as postoperative surveillance after colorectal surgery, post-polypectomy follow-up, or treatment of histologically confirmed polyps
• Patients with highly suspected or pathologically confirmed colorectal cancer
• Patients presenting with alarm symptoms or signs (hematochezia, melena, unexplained anemia or weight loss, palpable abdominal mass, or a positive digital rectal examination)
• Pregnant or breastfeeding women
• Patients with gastrointestinal obstruction
• Patients with inflammatory bowel disease, familial adenomatous polyposis, or serrated polyposis syndrome
• Patients who have taken anticoagulants (e.g., aspirin, warfarin) within 7 days before colonoscopy or who have coagulation disorders
• Patients currently enrolled in another clinical study or who participated in any clinical trial within the past 60 days
• Insertion failure for any reason (e.g., scope cannot pass an obstruction, patient cannot tolerate the procedure) or colonoscopy not reaching the cecum
• A Boston Bowel Preparation Scale (BBPS) score < 6 at scope insertion (inadequate preparation requiring repeat bowel cleansing)
• Use of non-guideline-recommended bowel preparation agents
• Patients undergoing emergency colonoscopy
• Inadequate withdrawal time (defined as a withdrawal time <6 minutes during the first examination or <2 minutes during the second examination)