Abstract
Annual as well as biennial screening for colorectal cancer has been proven effective for decreasing the mortality rate. We investigated the effect of changing the screening interval from one year to two years on tumor detection. We obtained data for invasive cancer found within two years of screening by cross-checking the regional cancer registry and prefecture-wide colorectal cancer screening of 246,660 individuals in Fukui prefecture between 1992 and 1998. Individuals diagnosed with cancer within one year of annual screening were defined as the annual group, and those diagnosed within one year of biennial screening or within one to two years of annual checkup were defined as the biennial group. The interval cancer rate and cumulative survival rate were compared between the two groups. In addition, the hazard rates for colorectal cancer mortality were compared using the Cox proportional hazards model.
The interval cancer rate in the biennial group (111 cases) was 40%, which was significantly higher than the 17% (p < 0.001) observed in the annual checkup group (90 cases). The five-year cumulative survival rate was 73.0% in the biennial group, which was significantly lower than that the 88.9% (p = 0.003) observed in the annual group. Furthermore, mortality risk was 2.3 times higher in the biennial group compared to the annual group (p = 0.043).
Therefore, it should be noted that changing the screening interval from one year to two years increases the interval cancer rate and is associated with a worse prognosis.
