A negative colonoscopy result is associated with a reduced risk of colorectal cancer for more than 12 years after the examination, compared with an unscreened population, new research has found.
In a retrospective cohort study published in JAMA Internal Medicine, researchers analyzed data from 1,251,318 individuals at average risk of colorectal cancer who were eligible to participate in screening over more than 9 million person-years of follow-up.
They found that screened individuals with a negative result had an adjusted 46%-95% lower risk of colorectal cancer and 29%-96% lower risk of colorectal cancer mortality than unscreened individuals across more than 12 years of follow-up.
At 10 years post colonoscopy, participants who had a negative colonoscopy result still had a significant 46% lower risk of colorectal cancer and 88% lower risk of colorectal cancer mortality. After more than 12 years, there was still a nonsignificant trend towards a lower risk of colorectal cancer incidence and mortality.
Jeffrey K. Lee, MD, of Kaiser Permanente San Francisco, and his coauthors suggested that their findings have implications for the timing of rescreening after a negative colonoscopy result.
“The current guideline-recommended 10-year rescreening interval is not based on a predetermined risk threshold, and while we observed a reduced risk of colorectal cancer and related deaths throughout the more than 12-year follow-up period, an examination of absolute risk [incidence] could provide another justification for the timing for rescreening,” they wrote. “Additional research is needed to evaluate the costs and benefits of earlier versus later rescreening, optimal rescreening tests following a negative colonoscopy result [e.g., another colonoscopy versus annual fecal immunochemical testing], and whether the benefits of rescreening vary between subgroups.”
The study showed that the rate of repeat endoscopic procedures increased at year 10, largely because of screening colonoscopies which are recommended at 10-year intervals. However in a separate analysis, the authors excluded colonoscopies for a screening indication and still found a similar reduction in the risk of colorectal cancer, compared with the unscreened group.
The data also showed a 22%-87% lower risk of proximal colorectal cancer, a 50%-99% lower risk of distal cancer, a 31%-95% lower risk of early-stage colorectal cancer, and a 56%-96% reduced risk of advanced-stage colorectal cancer among those who had a negative result, compared with those who did not undergo screening.
The authors wrote that this pattern of greater risk reductions in the distal versus proximal cancer had been seen in previous studies and could be the result of incomplete examinations, inadequate bowel cleansing, challenges in identifying right colon polyps and sessile serrated adenomas, or differences in polyp biology in the proximal versus distal colon.
The incidence rates of colorectal cancer among those who had a negative result from colonoscopy ranged from 16.6 per 100,000 person-years at 1 year after screening to 133.2 per 100,000 person-years at the 10-year mark. In comparison, the incidence rates among the unscreened population increased from 62.9 per 100,000 person-years at year 1 to 224.8 after year 12.
Mortality rates from colorectal cancer at year 1 were 6.8 per 100,000 person-years in the negative results group and 10.5 in the unscreened cohort. At year 12, that figure was 92.2 per 100,000 person-years in the negative results cohort, while after year 12 in the unscreened cohort, colorectal cancer mortality rates increased to 192 per 100,000 person years.
While the study made use of a validated cancer registry to ensure they accurately captured cancers and mortality, the authors acknowledged that they weren’t able to adjust for residual confounding factors such as red-meat intake or smoking.
The study was supported by the National Cancer Institute, the American Gastroenterological Association, and the Sylvia Allison Kaplan Foundation. No conflicts of interest were reported.
SOURCE: Lee JK et al. JAMA Intern Med. 2018 Dec 17. doi: 10.1001/jamainternmed.2018.5565.
