Objectives: Improved understanding of the subsequent risk death from colorectal cancer (CRC) among individuals who had adenomas removed is needed. We aimed to quantify this risk using prospectively collected data from population-based cohorts.
Materials and methods: Using Norwegian and Swedish registries, a cohort of 90,864 individuals with colorectal adenomas removed between 1980 and 2013 was identified. Surveillance was only recommended for high-risk adenomas. The validity of the registry data did not allow classification into low- and high-risk adenomas. Virtually complete follow-up was achieved through linkage to nationwide registers. We calculated incidence-based standardised mortality ratios (SMRs) with 95% confidence intervals (CI).
Results: The median follow-up was 7.2 years; 48,058 individuals were followed for more than 10 years. We observed 819 deaths (0.9%) from CRC and expected 731 CRC deaths (0.8%), corresponding to an absolute excess risk of 88 cases (0.1%) and a relative risk of 12% (SMR 1.12; 95%CI 1.05-1.20). The relative risk of CRC death following adenoma removal was slightly higher in Sweden (SMR 1.22; 95%CI 1.11-1.34) than in Norway (SMR 1.03; 95%CI 0.93-1.14), and higher in women (SMR 1.24; 95%CI 1.12-1.36) than in men (SMR 1.02; 95%CI 0.93-1.13). Among individuals with more than 10 years of follow-up, the estimates were similar to the overall cohort, absolute excess risk 0.1% (SMR 1.15; 95%CI 1.06-1.24).
Conclusion: The excess risk of CRC death following adenoma removal is small. Optimal surveillance recommendations should be tested in randomised trials.
Keywords: Mortality; adenoma; colorectal cancer; risk classification; standardised mortality ratio; surveillance.