Background: Several randomized studies have shown that colorectal cancer (CRC) screening by faecal occult blood test (FOBT) reduces CRC mortality. These trials have different designs, especially concerning FOBT frequency and duration, as well as the length of follow-up after stopping FOBT campaigns.
Aims: To review the effectiveness of screening for CRC with FOBT, to consider the reduction in mortality during or after screening or to identify factors associated with a significant mortality reduction.
Methods: A systematic review of trials of FOBT screening with a meta-analysis of four controlled trials selected for their biennial and population-based design. The main outcome measurements were mortality relative risk (RR) and 95% confidence interval (CI) of biennial FOBT during short (10 years, i.e. five or six rounds) or long-term (six or more rounds) screening periods, as well as after stopping screening and follow-up during 5-7 years. The meta-analysis used the Mantel-Haenszel method with fixed effects when the heterogeneity test was not significant, and used 'intent to screen' results.
Results: Although the quality of the four trials was high, only three were randomized, and one used rehydrated biennial FOBT associated with a high colonoscopy rate (28%). A meta-analysis of mortality results showed that subjects allocated to screening had a reduction of CRC mortality during a 10-year period (RR 0.86; CI 0.79-0.94) although CRC mortality was not decreased during the 5-7 years after the 10-year (six rounds) screening period, nor in the last phase (8-16 years after the onset of screening) of a long-term (16 years or nine rounds) biennial screening. Whatever the design of the period of ongoing FOBT, CRC incidence neither decreased nor increased, although it was reduced for 5-7 years after the 10-year screening period. Neither the design nor the clinical or demographic parameters of these trials were independently associated with CRC mortality reduction.
Conclusion: Biennial FOBT decreased CRC mortality by 14% when performed over 10 years, without evidence-based benefit on CRC mortality when performed over a longer period. No independent predictors of CRC mortality reduction have been identified in order to allow a CRC screening programme in any subgroups of subjects at risk.