Average risk people who underwent negative colonoscopies had a substantially lower risk of developing colorectal cancer, and dying from the disease, compared with unscreened patients, according to researchers.
At 10 years after screening — the current guideline-recommended re-screening interval — the risk for colorectal cancer and related deaths was 46% and 88% lower in patients who underwent colonoscopy, respectively, versus patients who were unscreened, reported Jeffrey Lee, MD, of Kaiser Permanente San Francisco, and colleagues in JAMA Internal Medicine.
“And we also saw a reduced risk of colorectal cancer and related deaths after at least 12 years of follow-up after the initial exam,” Lee MedPage Today.
“When I perform colonoscopies, my patients ask when they should come back if their colonoscopy is completely normal,” he explained. “According to the guidelines, we recommend a 10-year re-screening interval after colonoscopy with normal findings. But, there is very little evidence informing this recommendation.”
Consequently, Lee and colleagues wanted to examine the long-term risk of colorectal cancer and related mortality after negative colonoscopies compared with the risks associated with no screening.
They conducted a retrospective cohort study of eligible health plan members of Kaiser Permanente Northern California. The study population consisted of people, ages 50 to 75 during Jan. 1, 1998 and Dec. 31, 2015, who were at average risk for colorectal cancer, and had never been screened for the disease.
For purposes of analysis, Lee’s group assessed screening as a time-varying exposure in which all the participants in the study contributed unscreened person time until they were screened (fecal test, sigmoidoscopy, or colonoscopy) or censored (died, diagnosed with colorectal cancer, had health plan membership terminated, or reached the end of the study).
If the screening resulted in a negative colonoscopy result, those participants contributed person time in the negative colonoscopy group until censored.
The authors identified 1,251,318 average-risk, screening eligible cohort members for analysis, who accounted for 9,339,345 person-years of follow-up. And among those participants contributing unscreened person-time, 5,743 cases of colorectal cancer were diagnosed, 31.7% of which were proximal, and 45.1% advanced stage.
Among 99.166 individuals who contributed 417,987 person-years in the negative colonoscopy group, 184 cases of colorectal cancer were diagnosed, 51.1% of which were proximal, and 49.5% advanced stage.
Lee’s group determined that among the unscreened cohort, colorectal cancer 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, versus the negative colonoscopy group, which saw incidence rates increase from 16.6 per 100,000 person-years in year 1 to a high of 133.2 per 100,000 person-years at year 10.
As for related mortality, the unscreened cohort’s incidence 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 versus an increase of 6.8 per 100,000 person-years at year 1 to 92.2 per 100,000 person-years in the negative colonoscopy group.
The authors observed that “although reductions in risks were attenuated with increasing years of follow-up, [individuals with negative colonoscopy results had] a 46% lower risk of colorectal cancer and 88% lower risk of related deaths at the current guideline-recommended 10-year rescreening interval.”
They also saw a reduced risk of colorectal cancer by colon site and cancer stage.
“Physicians and patients should feel confident following the guideline-recommended re-screening interval after normal colonoscopy,” Lee told MedPage Today. “But our study also provides additional data for guideline developers on the possibility of extending the rescreening interval, given that the risk of colorectal cancer and related deaths remained reduced for more than 12 years after a normal colonoscopy. So, based on our findings, it’s potentially time to revisit the guidelines in terms of looking at the long-term risks.”
A study limitation was the possibility of residual confounding inherent to observational studies.
The study was supported by the National Cancer Institute-funded Population-Based Research Optimizing Screening Through Personalized Regimens consortium and the Sylvia Allison Kaplan Foundation.
Lee disclosed support from the NCI and the American Gastroenterological Association Research Scholar Award. Lee and co-authors disclosed no relevant relationships with industry.