A Cochrane review [Abstract] 1 included nine studies with a total of 744 386 participants (338 467 in screening and 405 919 in control group) to compare the effectiveness of screening for colorectal cancer (CRC) with flexible sigmoidoscopy to faecal occult blood testing (FOBT). Five studies compared sigmoidoscopy to no screening and four studies compared repetitive FOBT (annually and biennially) to no screening. Length of follow-up varied significantly between studies, ranging from a median of 6 years to 19.5 years.
The effects of screening on CRC incidence and mortality and all-cause mortality are given in table 1. Both flexible sigmoidoscopy and faecal occult blood testing reduce disease specific CRC mortality when applied as screening tools.
| Outcome | Relative effect(95% CI) | Assumed risk (no screening) | Corresponding risk (screening) | Number of participants (studies) |
|---|---|---|---|---|
| CRC mortality - flexible sigmoidoscopy | RR 0,72 (0.65 to 0.79) | 8 per 1000 | 6 per 1000(5 to 6) | 414 744(5) |
| CRC mortality - FOBT | RR 0,86 (0.80 to 0.92) | 8 per 1000 | 7 per 1000(6 to 7) | 329 642(4) |
| CRC incidence - flexible sigmoidoscopy | RR 0,82 (0.73 to 0.90) | 20 per 1000 | 16 per 1000(15 to 18) | 414 744(5) |
| CRC incidence - FOBT | RR 0,95 (0,88 to 1,02) | 20 per 1000 | 19 per 1000(18 to 20) | 329 536(4 ) |
| All-cause mortality - flexible sigmoidoscopy | RR 0,98 (0.95 to 1.01) | 254 per 1000 | 249 per 1000(241 to 257) | 364 827(4) |
| All-cause mortality - FOBT | RR 1,00 (0,99 to 1,01) | 254 per 1000 | 254 per 1000(251 to 257) | 329 642(4) |
When a multiple-treatment meta-analysis (MTM) was performed, a non-significant estimated effect of 15% reduction (95% CI: 1% increase to 28% reduction) was detected in CRC mortality when screening with flexible sigmoidoscopy was compared to annual or biennial FOBT.
The rates of major physical complications in the flexible sigmoidoscopy groups was 8 in 10 000. Psychological effects of screening were addressed in several trials. Acceptance among screened persons was very high. Worry associated with the invitation or positive screening results, if present, was generally of short duration. Short-term effects on lifestyle and health attitudes were addressed in two reports and no negative effects were detected. Adverse effects on lifestyle were evaluated prospectively in a randomized controlled study within the NORCCAP trial. Three years after screening, attendees were more likely to gain weight and were less likely to stop smoking, engage in physical activity and eat fruit and vegetables compared to a randomly chosen sample from the control group. All these comparisons reached statistical significance.
Colonoscopy or computed tomography colonography have mostly replaced sigmoidoscopy as the intervention of choice.
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