A study on the efficacy of a screening program for colorectal cancer in a small Japanese village.

A longitudinal study of the reduction in mortality was carried out to evaluate the efficacy of screening for colorectal cancer. A population-based screening program using the fecal occult blood test was conducted from 1982 to 1991 in the small village of Asahi, Nagano, Japan (index area). The efficacy of the screening program was measured by the standardized mortality ratio (SMR) for colorectal cancer. The SMR in the index area was 150 before screening (1972-1981) and 54 during screening (1982-1991). In addition to a significantly lower SMR in the latter period (P < 0.01), the change in the relative incidence--(D-B)/B, where D is the SMR during screening, and B is the SMR before screening--showed a 64% reduction. The SMR in Asahi was also compared with that in four neighboring villages (control area) not covered by the screening. The SMR in the control area was 133 before and 121 during screening, for a (D-B)/B value of -9%. The reduction in the relative incidence of colorectal cancer was thus significantly higher in the index area than in the control area (P < 0.01). These results confirm that the screening program conducted in the index area was effective as a preventive community measure in reducing mortality from colorectal cancer, and that the time trend assessment employed here is a useful method for evaluating the efficacy of cancer screening.