Akita Japan population-based colonoscopy screening trial: report of initial colonoscopy

Objective To assess the safety and quality of baseline screening colonoscopy in a randomised controlled trial (RCT). Methods A population-based RCT with an explanatory design is ongoing to evaluate the efficacy of colonoscopy screening in 9751 men and women aged 40–74 years at average risk of colorectal cancer (CRC) in Japan. Screening colonoscopies for the intervention group were performed from June 2009 to June 2017. Results Of the 4861 participants in the intervention group, 4495 (92.5%) underwent screening colonoscopy. The quality of bowel preparation was excellent (34.8%) or good (45.6%) in 80.4% of cases. The caecal intubation rate was 99.7% (4483/4495), and the mean (±SD) withdrawal time was 9.7 (±5.3) min. The adenoma detection rate (ADR) was 39.4% (1770/4495). A total of 27 participants (0.6%) were diagnosed with CRC, and 266 (5.9%) were diagnosed with advanced neoplasia (AN). In women, adenomas were more frequently detected in the proximal colon than in the distal colon (proximal: 18.9% vs distal: 16.4%, p=0.024), and a similar trend was observed for AN (proximal: 2.4% vs distal: 1.5%, p=0.045). No serious adverse events related to screening colonoscopy were reported, and minor adverse events were observed in two participants (0.04%). Conclusions Adequate performance in compliance, ADR, and safety was confirmed in the intervention arm of the RCT evaluating the efficacy of screening colonoscopy. The high quality of screening colonoscopy observed in the trial suggests its feasibility as a population-based screening approach. Trial registration number UMIN000001980.