Following high-risk adenoma removal, waiting five years instead of three for a first surveillance colonoscopy did not increase colorectal cancer incidence, according to an international study published in The New England Journal of Medicine.
The study, which was conducted by research teams across eight European countries including Spain and Norway, evaluated 10,799 patients who had high-risk adenomas removed. The findings come from an interim analysis of a 10-year study, and researchers noted that the results do not mean all patients can automatically extend their screening intervals to five years.
Study Design and Patient Allocation
Researchers randomly assigned the participants into two distinct groups. One group of 5,398 patients was scheduled for their first surveillance colonoscopy five years after polyp removal. Another group of 5,401 patients was scheduled for an initial check 3 years after the procedure, followed by an additional colonoscopy at the five-year mark.
High-risk adenomas in the study were strictly defined as cases featuring at least one adenoma measuring 10 millimeters or larger, severe cellular changes known as high-grade dysplasia, a villous structure, or a total count of three to 10 adenomas.
Cumulative Incidence and Statistical Findings
At the five-year point following polyp removal, the cumulative incidence of colorectal cancer was 0.77% in the five-year group and 0.82% in the three-year group. This left the five-year group with an incidence rate that was 0.05 percentage points lower, translating to roughly 77 versus 82 individuals per 10,000 patients.
Statistical analysis showed that the upper limit of the confidence interval for the difference between the two groups reached 0.68 percentage points, which remained below the prespecified noninferiority margin of 0.7 percentage points. Furthermore, no major differences were detected between the two groups when examining the disease stage at the time of cancer diagnosis. A total of five patients died from colorectal cancer, consisting of three patients (0.06%) in the five-year group and two patients (0.04%) in the three-year group, though researchers cautioned that the low number of deaths prevents definitive conclusions regarding safety equivalence.
Next Steps and Future Evaluation
Because the current data represents an interim analysis based on a mean follow-up of 5.5 years, researchers emphasize that the primary endpoint remains the cumulative colorectal cancer incidence at 10 years post-polyp removal. The research team stated that initiating surveillance colonoscopy five years after polyp removal was not inferior to starting at three years, clarifying that this means the five-year interval is not disadvantageous beyond the permitted margin rather than superior. The final outcomes of the ongoing 10-year tracking study will be necessary to establish long-term risk differences.
