Flexible Sigmoidoscopy Reduces Risk of Mortality in CRC Patients

A re-analysis of the 2016 US Preventive Services Task Force (USPSTF) evidence report on colorectal cancer (CRC) screening found that flexible sigmoidoscopy is associated with a lower risk of mortality from CRC. This finding contradicts the USPSTF’s previous conclusion that no methods of CRC screening can reduce all-cause mortality.

After an initial review of the Norwegian Colorectal Cancer Prevention (NORCCAP) study that aggregated results from 2 different age cohorts, the USPSTF had previously concluded that no CRC screening methods were associated with a lower risk of mortality. However, the researchers realized that aggregating the results of the cohorts, whom had notable differences, may have created a Simpson paradox in the initial meta-analysis.
_____________________________________________________________________________________________________

RELATED CONTENT
Patient Education, Support May Increase CRC Screening
Diet Quality Linked to Colorectal Cancer Risk
_____________________________________________________________________________________________________

In order to re-analyze the effect of CRC screening on the risk of mortality in each cohort, the researchers separately evaluated the younger cohort of patients aged 50 to 54 years and the older cohort of patients aged 55 to 64 years, along with data from the 4 studies cited in the 2016 USPSTF evidence report. Additionally, a sensitivity analysis was conducted via multiple random-effects models.

Results of the re-analysis indicated that the risk of all-cause mortality was lower in the younger cohort than in the older cohort. Additionally, after a separate analysis of each cohort, the researchers found that flexible sigmoidoscopy reduced the risk of all-cause mortality at 11 to 12 years after diagnosis. At 11.5 years of follow-up, the absolute risk reduction of death in patients aged 50 to 74 years was 3 deaths per 1000 individuals who were screened.

“Screening with flexible sigmoidoscopy reduces all-cause mortality with an absolute risk reduction that is clinically important relative to other preventive interventions,” the researchers concluded. “Aggregation of outcomes of the NORCCAP study in the USPSTF evidence report created a Simpson paradox that obscured the reduction in all-cause mortality by changing 2 statistically nonsignificant reductions into a statistically significant increase. This effect was large enough to nullify the reductions in all-cause mortality of the other trials in the meta-analysis.”

—Christina Vogt

Reference:

Swartz AW, Eberth JM, Josey MJ, Strayer SM. Re-analysis of all-cause mortality in the U.S. Preventive Services Task Force 2016 evidence report on colorectal cancer screening [Published online August 22, 2017]. Ann Intern Med. doi: 10.7326/M17-0859.