Current guidelines suggest a 5-year interval for colorectal cancer (CRC) screening by sigmoidoscopy. However, the optimal screening interval is uncertain.
Researchers in America estimated the annual incidence of distal and proximal CRC in the first 5 years following a negative sigmoidoscopy examination to gauge the potential benefit of rescreening in less than 5 years.
| Distal CRC incidence:|
2.8 per 100,000 person years 1 year after follow-up13.0 per 100,000 person years 4 years after follow-up
The group used computerized databases to identify a cohort of 72,483 participants taking part in a Colon Cancer Prevention program in Northern California.
Included in the study were men and women aged 50 years and older who had a negative screening flexible sigmoidoscopy examination between 1994 and 1996 and were considered not to be at high risk for developing CRC.
Subjects were censored at the time of diagnosis (for cases), death, termination of their membership of the colon cancer prevention program, or subsequent colon examination.
30 cases of distal and 80 cases of proximal CRC occurred.
Age-adjusted incidence rates of distal CRC ranged from a low of 2.8 per 100,000 person-years in the first year of follow-up to a high of 13.0 per 100,000 in the fourth year.
However, for the entire follow-up period, incidence of distal CRC remained much lower than age-adjusted rates of 70.6 in the general population.
The incidence of proximal CRC was also decreased modestly over population rates of disease.
The team concluded that screening by sigmoidoscopy more frequently than every 5 years would likely lead, at best, to only modest improvements as compared with a 5-year screening interval.