Colorectal Cancer Screening (PDQ®): Screening - Health Professional Information [NCI] - Evidence of Benefit
Table 3. Randomized Controlled Screening Trials: Fecal Occult Blood Testing continued...
The flexible fiberoptic sigmoidoscope was introduced in 1969. The 60 cm flexible sigmoidoscope became available in 1976. The flexible sigmoidoscope permits a more complete examination of the distal colon with more acceptable patient tolerance than the older rigid sigmoidoscope. The rigid instrument can discover 25% of polyps, and the 60 cm scope can find as many as 65%. The finding of an adenoma by FS may warrant colonoscopy to evaluate the more proximal portion of the colon.[39,40] The prevalence of advanced proximal neoplasia is increased in patients with a villous or tubulovillous adenoma distally and is also increased in those aged 65 years or older with a positive family history of CRC and with multiple distal adenomas. Most of these adenomas are polypoid, flat and depressed lesions, which may be somewhat more prevalent than previously recognized.
Five sigmoidoscopy screening RCTs have reported incidence and mortality results. These are the Norwegian Colorectal Cancer Prevention (NORCCAP) trial; the Telemark trial in Norway; the United Kingdom trial; the SCORE trial in Italy; and the U.S. Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial. Participants were aged 50 to 59 years in the Telemark trial, aged 55 to 74 years in PLCO, and aged 55 to 64 years in the other three trials. Together the trials enrolled 166,000 participants in the screened groups and 250,000 participants in the control groups. Follow-up ranged from 6 to 13 years. Results were summarized in two systematic reviews. There was an overall 28% relative reduction in CRC mortality (RR, 0.72; 95% CI, 0.65-0.80), an 18% relative reduction in CRC incidence (RR, 0.82; 95% CI, 0.73-0.91), and a 33% relative reduction in the incidence of left-sided CRC (RR, 0.67; 95% CI, 0.59-0.76). There was no effect on all-cause mortality.[43,44]
Two case-control studies have been reported that evaluate the efficacy of screening sigmoidoscopy in preventing CRC mortality;[45,46] one study used rigid sigmoidoscopy, and the other used rigid and FS. Both studies were conducted in prepaid health plans and suggested a significantly decreased risk (70%-90%) of fatal cancer of the distal colon or rectum among individuals with a history of one or more sigmoidoscopic examinations compared with nonscreened patients.