A single, high-quality negative screening colonoscopy was associated with reduced incidence of or death from colorectal cancer for more than 17 years, an observational study found.
Researchers reviewed data from the Polish Colonoscopy Screening Program on average-risk individuals ages 50 to 66 years who had a single negative colonoscopy (no neoplastic findings) between October 2000 and December 2011. In the screening program, primary screening colonoscopy is offered to asymptomatic average-risk individuals ages 50 to 66 years in the opportunistic setting every 10 years or once per lifetime via a mailed invitation, which was introduced in 2014. High-quality colonoscopy included a complete examination, with adequate bowel preparation, performed by endoscopists with an adenoma detection rate of 20% or greater.
All patients underwent opportunistic screening colonoscopy, defined as participation advised by general or family practitioners. After screening in the opportunistic setting, they were excluded from the invitation-based screening program and could not receive a second screening colonoscopy through the invitation-based program. Only participants who were still in the screening age range after 10 years could receive a second screening colonoscopy in the opportunistic setting.
The study cohort was followed for colorectal cancer incidence and death by national registries and linked databases. Researchers assessed standardized incidence ratios (SIRs) and standardized mortality ratios (SMRs). Results were published May 26 by Annals of Internal Medicine.
Among 165,887 individuals followed for up to 17.4 years, colorectal cancer incidence (0.28; 95% CI, 0.25 to 0.30) and mortality (0.19; 95% CI, 0.16 to 0.21) were 72% and 81% lower, respectively, than in the general population. High-quality examination resulted in twofold lower incidence (SIR, 0.16; 95% CI, 0.13 to 0.20) and mortality (SMR, 0.10; 95% CI, 0.06 to 0.14) than low-quality examination (SIR, 0.32 [95% CI, 0.29 to 0.35]; SMR, 0.22 [95% CI, 0.18 to 0.25]).
In multivariable analysis, hazard ratios for cancer incidence after high-quality versus low-quality colonoscopy were 0.55 (95% CI, 0.35 to 0.86) for 0 to 5 years, 0.54 (95% CI, 0.38 to 0.77) for 5.1 to 10 years, and 0.46 (95% CI, 0.25 to 0.86) for 10 to 17.4 years. Only after high-quality colonoscopy did the SIR and SMR for 10.1 to 17.4 years of follow-up not differ compared with earlier observation periods.
“High quality was key for the profound long-term efficacy of screening colonoscopy in the proximal colon, and among women,” the authors wrote. “These findings are of paramount importance, because previous reports have questioned the efficacy of colonoscopy in the proximal colon and of screening sigmoidoscopy in women.”
The findings also suggest that for up to 17.4 years after a negative colonoscopy, many cases of colorectal cancer arise from lesions missed during the examination instead of new lesions. Although zero risk cannot be proven, subsequent screening at 10 years may add little to the more than 80% reduction in risk, and the very low 15-year risk of 0.24%, after high-quality baseline examination, the authors said.
“Each component of high-quality examination—cecal intubation, adequate bowel preparation, and ADR [adenoma detection rate] of 20% or greater—contributed to the observed colonoscopy efficacy, with ADR being most important,” they wrote. “Of note, use of ADR cutoffs of 15% to 30% did not substantially change our main findings.”