In contrast, patients with high-risk adenomas at baseline had significantly elevated rates of both CRC and CRC-related death, reported lead author Jeffrey K. Lee, MD, of Kaiser Permanente San Francisco and colleagues.
With additional research, these findings may influence colonoscopy surveillance intervals, the investigators wrote in Gastroenterology.
“Current guidelines recommend that patients with a low-risk adenoma finding ... receive surveillance colonoscopy in 5-10 years, although in practice, clinicians often use even more frequent surveillance ... in this low-risk group,” they wrote. “The rationale for continued support of shorter-than-recommended surveillance intervals for patients with low-risk adenomas is unclear, but could stem from a lack of long-term population-based studies assessing colorectal cancer incidence and related deaths following low-risk adenoma removal or randomized trials evaluating optimal postpolypectomy surveillance intervals.”
To alleviate this knowledge gap, the investigators began by screening data from 186,046 patients who underwent baseline colonoscopy between 2004 and 2010 at 21 medical centers in California. Following exclusions based on family history, confounding gastrointestinal diseases, and incomplete data, 64,422 patients remained. Among these patients, the mean age was 61.6 years, with a slight female majority (54.3%). Almost three out of four patients (71.2%) had normal colonoscopy findings, followed by smaller proportions who were diagnosed with low-risk adenoma (17.0%) or high-risk adenoma (11.7%), based on United States Multi-Society Task Force guidelines.
After a median follow-up of 8.1 years, 117 patients who had normal colonoscopy findings developed CRC, 22 of whom died from the disease. In comparison, the low-risk adenoma group had 37 cases of CRC and 3 instances of CRC-related death, whereas the high-risk adenoma group had 60 cases of CRC and 13 instances of CRC-related death.
In the no-adenoma and low-risk groups, trends in age-adjusted CRC incidence rates were similar; in both cohorts, CRC incidence increased gradually over the decade following colonoscopy, with each group reaching approximately 50 cases per 100,000 person-years by year 10. In contrast, CRC incidence climbed rapidly in the high-risk adenoma group, ultimately peaking a decade later at almost 220 cases per 100,000 person-years. Average incidence rates per 100,000 person-years were similar among patients with no adenoma (31.1) and low-risk adenoma (38.8), but markedly higher among those with high-risk adenoma (90.8). At the end of the 14-year follow-up period, absolute risks of CRC among patients with no adenoma, low-risk adenoma, and high-risk adenoma were 0.51%, 0.57%, and 2.03%, respectively.
Based on covariate-adjusted Cox regression models, patients with low-risk adenoma did not have a significantly higher risk of CRC or CRC-related death than did patients with no adenoma. In contrast, patients with high-risk adenoma had significantly higher risks of CRC (hazard ratio, 2.61) and CRC-related death (HR, 3.94).
“These findings support guideline recommendations for intensive colonoscopy surveillance in [patients with high-risk adenomas at baseline],” the investigators wrote.
Considering similar risks between patients with low-risk adenomas and those with normal findings, the investigators suggested that longer surveillance intervals may be acceptable for both of these patient populations.
“Guidelines recommending comparable follow-up for low-risk adenomas and normal examinations, such as lengthening the surveillance interval to more than 5 years and possibly 10 years, may provide comparable cancer incidence and mortality benefits for these two groups,” they wrote.
Still, the investigators noted that study limitations – such as disparate rates of subsequent colonoscopy between groups – make it difficult to draw definitive, practice-changing conclusions.
“Additional studies, potentially including randomized trials, on the natural history of low-risk adenoma and normal findings without intervening surveillance exams before 10 years are needed to help guide future surveillance practices,” they concluded.
The study was supported by the National Cancer Institute and the American Gastroenterological Association. The investigators disclosed no conflicts of interest.
SOURCE: Lee JK et al. Gastroenterology. 2019 Oct 4. doi: 10.1053/j.gastro.2019.09.039.
