A U.S. Trial of Flexible Sigmoidoscopy for Colorectal Cancer Screening

Screening lowered both cancer incidence and cancer-specific mortality.

In the colorectal cancer screening arm of the U.S. Prostate, Lung, Colorectal, and Ovarian (PLCO) trial, 156,000 people (age range, 55–74) were randomized to either flexible sigmoidoscopy (with a second screening 3 or 5 years later) or usual care. The researchers now report outcomes after a median follow-up of 12 years.


Compared with the usual-care group, the screening group had significantly lower colorectal cancer incidence (about 1.66% vs. 1.31%) and cancer-specific mortality (about 0.44% vs. 0.33%). For distal cancer, screening reduced both incidence and mortality; for proximal cancer, screening was associated with reduced incidence but not mortality.

Other important aspects of the study are as follows:

•     Only 84% of people assigned to screening actually underwent a first screening, and only 54% underwent subsequent screening.

•     29% of those in the screening group had a polyp or mass noted on sigmoidoscopy; only three quarters underwent colonoscopy for further evaluation of the sigmoidoscopic abnormality.

•     Perforation occurred in 1 per 36,000 sigmoidoscopies and in 1 per 930 colonoscopies performed to follow-up a sigmoidoscopic abnormality.

•     "Contamination" was substantial: 34% of usual-care participants underwent colonoscopy during the first 5 years of follow-up.

•     The number invited to screening to prevent one case of colorectal cancer was 282; the number invited to screening to prevent one colorectal cancer death was 871.

Citation(s):

Schoen RE et al. Colorectal-cancer incidence and mortality with screening flexible sigmoidoscopy. N Engl J Med 2012 Jun 21; 366:2345.

Inadomi JM. Why you should care about screening flexible sigmoidoscopy. N Engl J Med 2012 Jun 21; 366:2421.