Colorectal cancers detected through screening are associated with lower stages and improved survival

Population screening for colorectal cancer (CRC) using faecal occult blood test (FOBT) will be introduced in Denmark in 2014. Prior to the implementation of the screening programme, a feasibility study was performed in 2005-2006. In this paper, occurrences of colorectal cancer in the feasibility study cohort were reviewed with respect to the effect of screening participation on stages and survival.

All cases of CRC in a feasibility study cohort diagnosed from the beginning of the study until two years after the study ended were identified. Differences in the distribution of colon cancer stages and rectal cancer groups between the various screening categories were analysed through χ(2)-tests. Survival analysis with respect to screening groups was done by Kaplan-Meier and Cox-Mantel hazard ratios, and survival was corrected for lead time.

Colon cancers detected through screening were diagnosed at significantly lower stages than among screening non-responders. There were relatively fewer locally advanced rectal cancers among patients diagnosed through positive FOBT than among non-responders. Survival among screening cancer patients was superior to that of all other screening groups. No effect of lead time was detected. Neither stage nor survival among patients who had a negative FOBT was inferior to the unscreened Danish population.

The positive effect on survival among screening cancer patients is neither outbalanced by more advanced cancers among FOBT-negative patients than among non-responders nor by risks reported for colonoscopy.

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