Negative Colonoscopy Linked to Lower CRC Risk, Death After 12 Years

December 20, 2018
Leah Lawrence

Negative colonoscopy results in patients with average CRC risk were associated with a lower risk for CRC diagnosis and death more than a decade after the test.

Negative colonoscopy results among patients with average risk for colorectal cancer were associated with a lower risk for colorectal cancer diagnosis and death more than a decade after the test compared with patients who had no screening, a retrospective study found.

“Current guidelines recommend a 10-year rescreening interval after a negative colonoscopy result…this recommendation is supported by modest empirical data,” wrote Jeffrey K. Lee, MD, of Kaiser Permanente San Francisco, and colleagues. “Our findings can inform guidelines recommendations for rescreening and future studies to evaluate the costs and benefits of earlier vs later rescreening intervals.”

The study looked at more than 1.2 million average-risk screening eligible patients aged 50 to 75 taken from an integrated healthcare delivery organization in Northern California. The researchers calculated hazard ratios [HR] for colorectal cancer and related deaths according to time since negative colonoscopy result or since cohort entry for those patients who were unscreened. The results were published in JAMA Internal Medicine.

Of the cohort, 5,743 cases of colorectal cancer were diagnosed during about 4.6 million person-years of follow-up. These included 31.7% proximal cancers, and 45.1% advanced-stage cancers. About 99,000 participants contributed to the negative colonoscopy cohort. Among this group, 184 colorectal cancers were diagnosed including 49.5% with advanced disease.

“The present study expands knowledge regarding risks of colorectal cancer and related deaths following a negative colonoscopy result by providing annual incidence and mortality rates for more than 12 years following a negative colonoscopy result and for those unscreened from the same background population,” the researchers wrote.

In the unscreened group, incidence rates increased with follow-up from 62.9 to 224.8 per 100,000 person years at more than 12 years. Mortality rates also increased from 10.5 per 100,000 in the first year to 192.0 per 100,000 person years at more than 12 years.

Rates also increased among those with negative colonoscopy results. Incidence rates increased from 16.6 to 133.2 per 100,000 person years in year 10, and mortality rates increased from 6.8 to 92.2 per 100,000 person years in year 12.

Compared with participants who were unscreened, screening with a negative result was associated with a 46% lower risk of colorectal cancer diagnosis (HR, 0.54; 95% CI, 0.31–0.94) and an 88% decreased risk for related deaths (HR, 0.12; 95% CI, 0.02–0.82) at the current guideline-recommended interval of 10 years.

“The magnitude of risk reduction for colorectal cancer incidence after negative colonoscopy results was greater in the distal than proximal colon, a pattern consistent with prior studies,” the researchers noted.

“Our study has policy implications on the timing of rescreening after a negative colonoscopy result,” they wrote. “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.”