Patients in Norway who underwent removal of low-risk colorectal adenomas but did not get further colonoscopic surveillance showed a 25% lower risk of death from colorectal cancer 8 years later, according to a report published online Aug. 28 in the New England Journal of Medicine.
"Thus, any increase in the risk of death from colorectal cancer associated with low-risk adenomas may have been eliminated by the polypectomy," said Dr. Magnus Løberg of the department of health management and health economics, University of Oslo, and his associates.
"Our finding that the removal of low-risk adenomas reduces the risk of death from colorectal cancer over a period of 8 years to a level below that of the general population is consistent with the hypothesis that surveillance every 5 years after removal of low-risk adenomas may confer little benefit over less intensive surveillance strategies. Furthermore, complications associated with colonoscopy are not trivial and might offset the benefit of surveillance" in this patient population, they noted.
Dr. Løberg and his colleagues took advantage of nationwide data in Norway’s cancer registry to "evaluate colorectal cancer mortality in a large, population-based cohort with virtually complete follow-up for death from colorectal cancer." They identified 40,826 patients aged 40 years and older who had at least one colorectal adenoma removed between 1993 and 2007. Surveillance colonoscopy was not recommended for such patients in Norway at that time.
A total of 49.8% had lesions classified as high risk because they showed a villous growth pattern or high-grade dysplasia, or because there were multiple adenomas. The remaining 50.2% of patients had lesions classified as low risk. Detailed information concerning polyp size and the exact number of polyps was not available to the researchers in their record search, so they could not classify the adenomas more definitively.
After a median follow-up of 7.7 years, 1,273 patients were diagnosed as having colorectal cancer, including 383 who died of the disease.
Among patients whose adenomas were low risk, colorectal cancer–specific mortality was reduced by 25%, compared with that of the general population, even though they had not undergone any further colonoscopic surveillance after the initial procedure, the investigators reported (N. Engl. J. Med. 2014 Aug. 28 [doi: 10.1056/NEJMoa1315870]).
In contrast, colorectal cancer–specific mortality was increased by 16% among patients whose adenomas were high risk – an excess of 33 deaths from the disease in this large cohort. "Our study cannot clarify the extent to which the increased risk after polypectomy reflects the underlying increase in the risk of death from colorectal cancer among these patients, but in any case, surveillance might not have been sufficient to lower this increased risk. This question can be answered only by performing comparative randomized trials with different surveillance intervals," Dr. Løberg and his associates said.
This study was supported by the Norwegian Cancer Society, the U.S.-Norway Fulbright Foundation for Educational Exchange, the Research Council of Norway, and the Karolinska Institute. Dr. Løberg reported no financial conflicts of interest; one of his associates reported ties to Exact Sciences, HJort/Norchip, CCS Pharma, and Fujinon.