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Patients with no family history of colorectal cancer (CRC) whose first colonoscopy was negative may be able to delay their next screening for 15 years rather than the currently recommended 10 years, a Swedish register-based cohort study showed.

For patients with a first colonoscopy negative for CRC, the 10-year standardized incidence ratio was 0.72 (95% CI 0.54-0.94) and the 10-year standardized mortality ratio was 0.55 (95% CI 0.29-0.94), reported Mahdi Fallah, MD, PhD, of the National Center for Tumor Diseases at the German Cancer Research Center in Heidelberg, and colleagues in .

"In other words, the 10-year cumulative risk of CRC in year 15 in the exposed group was 72% that of the 10-year cumulative risk of CRC in the control group," they wrote. "Extending the colonoscopy screening interval in individuals with a first colonoscopy with findings negative for CRC could miss the early detection of only two CRC cases and the prevention of one CRC-specific death per 1,000 individuals, while potentially avoiding 1,000 colonoscopies."

A sensitivity analysis that included only colonoscopies performed from 1990 through 2000 "slightly extended the period of significantly lower risk to 16 years," Fallah and team noted, while adjusting for additional risk factors including obesity, chronic obstructive pulmonary disease, alcohol use disorder, and diabetes did not change the results (16 and 15 years for CRC and CRC-specific death, respectively).

With longer screening intervals of 16 to 20 years, additional CRC diagnoses per 1,000 individuals increased gradually from 4.5 at 16 years to 11.9 cases at 20 years, while additional CRC-specific deaths per 1,000 individuals increased from 2.0 to 3.6 at those time points.

"Compared with that could provide only an estimated minimum interval between colonoscopy screenings, the current study has the longest follow-up time, and to our knowledge, this is the first study to observe a point at which the reduced risk of CRC in the exposed group reached the level of CRC risk in the control group," the authors wrote. "Together with identifying harms of a longer interval, this finding allowed us to determine an optimal time for a second colonoscopy based on a large and long-lasting dataset."

, Rashid N. Lui, MBChB, of the Chinese University of Hong Kong, and Andrew T. Chan, MD, MPH, of Massachusetts General Hospital and Harvard University in Boston, noted that this study "adds to an evolving body of evidence that supports extending the historical 10-year screening interval for individuals at average risk of CRC."

"Conducting a randomized clinical trial comparing different screening intervals would be challenging, given the need for a large population and long duration of follow-up; therefore, analyses that leverage large, well-curated, population-based registries, such as this one ... are the best available evidence to address this important clinical question," they added.

"Taken together with prior studies, future screening guidelines in many parts of the world may warrant revision," they concluded. "Such a change may have important implications for economic modeling comparing the resources required for colonoscopy-based screening programs with noninvasive options."

For this study, Fallah and team used data from a Swedish nationwide register from 1990 to 2016 to compare 110,074 participants who had a first colonoscopy with findings negative for CRC at ages 45 to 69 years (exposed group) with 1,981,332 controls matched by sex, birth year, and baseline age who either did not have a colonoscopy during follow-up or underwent colonoscopy that resulted in a CRC diagnosis. Baseline characteristics were comparable between the two groups. Average age was 59, and 59% of both groups were women.

During up to 29 years of follow-up for patients with a first colonoscopy with findings negative for CRC, 484 incident CRCs and 112 CRC-specific deaths occurred.

The authors acknowledged limitations to their study, including the inability to adjust for some confounding factors, such as colonoscopy quality and comorbidities, and the inclusion of primarily white individuals, which limits generalizability of the findings.

The editorialists also noted that this study was based on data collected in European populations. "Validation of these results in other settings is critical to generalize these findings globally, including parts of the world, such as Asia, in which widespread CRC screening has begun more recently," they wrote. "Not only is it possible that the timing of the adenoma-carcinoma sequence may differ in non-European populations, but variation in the background incidence of CRC will significantly impact the number of incident CRCs prevented associated with a given screening interval."

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