Clinical epidemiological study on a rational screening program for colorectal cancer

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The present study was intended to evaluate efficacy of screening program for colorectal cancer(CRC) using the two-day immunochemical fecal occult blood test(IFOBT). It was shown that risk of dying of CRC reduced after screening. Approximately 50 to 70% of risk reduction was suggested for those screened within the past 5 years, ie odds ratios for those screened 1 to 5 years before case diagnosis ranged 0.33(95% confidence interval: 0.13-0.84) to 0.52(0.27-1.01). By comparing screening histories between incident CRC cases in the study areas during the same time period and their controls, self-selection bias was estimated as incidence ratio of CRC: incidence in screening responders to that in non-responders. Incidence ratio in the late phase after screening, which would be an approximate value of self-selection bias, was not less than 1.0 showing that self-selection bias was not a significant contributor to the low odds ratios obtained in the main analysis of the present study. These results indicate that CRC screening program with IFOBT can reduce mortality from the cancer.