A study in The New England Journal of Medicine found the risk reduction for those who were invited to receive a colonoscopy screening compared those who did not to be just 18 percent — but those who actually underwent the procedure saw larger reductions.
The study was a randomized trial that took place between 2009 and 2014. It involved healthy men and women 55 to 64 years of age from Poland, Norway, Sweden and the Netherlands. Participants were randomly assigned in a 1:2 ratio to a group invited to undergo a screening colonoscopy and another group not invited to receive a screening. Read more about the methodology here.
Follow-up data was available for 84,585 participants in Poland, Norway and Sweden. Of those invited to participate in the colonoscopy, 42 percent underwent the screening.
The study found that during a median follow-up of 10 years, 259 cases of colorectal cancer were diagnosed in the group that was invited to be screened compared with 622 cases in the group that did not. At 10 years, the group that was invited to be screened had a risk of colorectal cancer of 0.98 percent compared to 1.2 percent in the group that was not screened — a risk reduction of 18 percent. The risk of death from colorectal cancer in the invited group was 0.28 percent and 0.31 in the unscreened group.
The study authors estimated that if everyone in the invited group had undergone a colonoscopy, the risk of colorectal cancer would fall from 1.22 percent to 0.84 percent — a decrease of about 31 percent. Colorectal cancer-related deaths would have fallen an estimated 50 percent, from 0.3 percent to 0.15 percent. However, the authors noted that these reductions were lower than anticipated.
The trial found that the risk of colorectal cancer at 10 years was still lower in participants invited to undergo screening colonoscopy than those who were not assigned a screening.