Screening for colorectal cancer (CRC) with a colonoscopy can reduce risks for disease-related mortality because it allows for precancerous adenomas to be detected and removed at an earlier, more treatable stage, but the timing of when colonoscopy is used varies widely throughout the United States.

“All average-risk patients who reach the age of 50 are recommended to undergo CRC screening,” says Jeffrey K. Lee, MD, MAS. “Current guidelines recommend rescreening patients every 10 years after a colonoscopy with normal findings. However, this recommendation is not based on evidence from randomized clinical trials that have focused on rescreening intervals.”


Taking a Closer Look

To better optimize CRC prevention and minimize the harm associated with colonoscopy, Dr. Lee and colleagues had a study published in JAMA Internal Medicine that sought to address the important question of when to rescreen patients after a normal colonoscopy. “Our hope was to find stronger evidence to guide clinicians and patients on the timing of when to rescreen after a colonoscopy with normal findings,” says Dr. Lee.

Authors of the analysis retrospectively examined the long-term risk of CRC and related deaths after a negative colonoscopy result and compared these data with no screening. The study, conducted in a large community-based setting, included more than 1.2 million average-risk screening-eligible patients (aged 50 to 75) from 1998 to 2015. Screenings were examined as a time-varying exposure in which all participants contributed person-time unscreened until they were either screened or censored. Hazard ratios were then calculated for CRC and related deaths according to time since receipt of a negative colonoscopy result.


Examining Key Findings

Among unscreened patients, CRC incidence rates increased with follow-up time from 62.9 per 100,000 person-years in year 1 to 224.8 per 100,000 person-years at more than 12 years. Related mortality rates increased from 10.5 per 100,000 person-years in year 1 to 192.0 per 100,000 person-years at more than 12 years.

“A colonoscopy with normal findings in average-risk patients was associated with a lower risk of CRC and related deaths for more than 12 years when compared with no screening,” Dr. Lee says (Figure). “In addition, average-risk patients with a normal colonoscopy had a 46% lower risk of CRC and an 88% lower risk of related death at the guideline-recommended 10-year rescreening interval.”

The study also noted that the magnitude of risk reduction for CRC incidence after negative colonoscopy results was greater in the distal than proximal colon. Potential explanations for this finding include:

  • Incomplete examinations and inadequate bowel cleansing of the right colon.
  • Difficulty identifying right colon conventional adenomas and serrated polyps.
  • Differences in proximal versus distal polyp biology.


Analyzing the Implications

The study by Dr. Lee and colleagues expands knowledge on the risks of CRC and related deaths following a negative colonoscopy result by providing annual incidence and mortality rates for more than 12 years. Based on the findings, a colonoscopy with normal findings appears to be associated with extended mortality protection.

“Clinicians should feel confident about the current guideline recommendations for a minimum 10-year interval for rescreening patients after a normal colonoscopy,” Dr. Lee says. “A minimum CRC rescreening interval should be conducted at 10 years or possibly longer after a normal colonoscopy. Discontinuing rescreening may be advised when managing patients who have less than a 10-year life expectancy.”

Additional research is needed to evaluate the costs and benefits of earlier versus later rescreening for CRC, optimal rescreening tests following a negative colonoscopy result, and whether the benefits of rescreening vary between patient subgroups. “Future research should also focus on an even longer period of follow-up after a normal colonoscopy to better understand its effect and durability on future CRC risk and related deaths,” says Dr. Lee. “In the meantime, our study findings may be used to inform guidelines for rescreening after a negative colonoscopy result.”