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CRC risk after negative screening higher at 6- to 10-year follow-up compared to first 5 years
During the 10 years following a negative screening sigmoidoscopy, the risk for colorectal cancer doubled in the second 5 years of follow-up, compared to the first 5 years. However, the risk remained lower than that of the population levels.
“These results will allow clinicians to provide estimates of the absolute risk of CRC following a negative screening sigmoidoscopy, and will inform the choice of appropriate screening interval,” the researchers wrote.
V. Paul Doria-Rose, MD, of the health services and economics branch, applied research program, division of cancer control and population sciences at the National Cancer Institute in Bethesda, Md., and colleagues, conducted a large cohort study to examine patterns in the incidence of CRC during the 10 years following a negative sigmoidoscopy examination.
The researchers included a total of 72,483 men and women in an integrated health care delivery organization in the San Francisco Bay area. The patients were aged older than 50 years and all had a negative screening sigmoidoscopy between 1994 and 1996. The researchers excluded patients who had inflammatory bowel disease, prior polyps or CRC, or a strong family history.
Standardized incidence ratios were used to compare incidence rates of distal and proximal CRC in the cohort to population levels in the San Francisco Bay area based on Surveillance, Epidemiology and End Results data. The researchers also calculated the rate ratios (RR) and rate differences (RD) between risk during the first 5 years after the negative screening and the second 5 years after the negative screening. The follow-up period was 10.5 years with a mean of 8.1 years per person in the study.
Data was examined on 103 cases of distal, and 333 cases of proximal colorectal adenocarcinomas that were diagnosed during the follow-up period.
Following a negative screening sigmoidoscopy, incidence rates of distal CRC in the cohort were lower than in the “population at large … for the entire follow-up period,” according to the researchers. However, rates still rose to a higher level in the study cohort as the years went by leading to rates that were twice as high at 6 to 10 years, compared to the 1- to 5-year follow-up rates (RR = 2.08, 95% CI, 1.38 to 3.16; RD: 14 per 100,000 person-years, 95% CI 6-22). Demographic and exam characteristic subgroups showed comparable patterns of increasing distal CRC incidence except for individuals aged younger than 60 years at baseline, for whom distal CRC rate was “fairly constant, and very low, over time.” Proximal CRC rates also followed a pattern of increasing over time.
“Based on these results, it does appear that there would be a modest number of cases of distal CRC that could be prevented by more frequent sigmoidoscopy (eg, every 5 years vs. every 10); the incidence of distal CRC was 14 per 100,000 greater during the second 5 years of follow-up,” the researchers wrote. “However, the potential to prevent at least some of these additional cases must be considered in light of the potential harms of sigmoidoscopy, as well as the additional costs of screening more frequently; in light of these potential harms/costs, 10 years may well be a rational option for interval for screening sigmoidoscopy.”
Disclosures: The researchers report no relevant financial disclosures.