Benefit of Biennial Fecal Occult Blood Screening on Colorectal Cancer in England: A Population-Based Case-Control Study

Abstract

Background: The English national bowel cancer screening program offering a guaiac fecal occult blood test began in July 2006. In randomized controlled trials of guaiac fecal occult blood test screening, reductions in mortality were accompanied by reductions in advanced stage colorectal cancer (CRC). We aimed to evaluate the effect of participation in the national bowel cancer screening program on stage-specific CRC incidence as a likely precursor of a mortality effect.

Methods: In this population-based case-control study, cases were individuals diagnosed with CRC aged 60-79 years between January 1, 2012, and December 31, 2013. Two controls per case were matched on geographic region, gender, date of birth, and year of first screening invitation. Screening histories were extracted from the screening database. Conditional logistic regression with correction for self-selection bias was used to estimate odds ratios (odds ratios corrected for self-selection bias [cOR]) and 95% confidence intervals (CIs) by Duke stage, sex, and age.

Results: 14 636 individuals with CRC and 29 036 without were eligible for analysis. The odds of CRC (any stage) were increased within 30 days of a screening test and decreased thereafter. No reduction in CRC (any stage) among screened individuals compared with those not screened was observed (cOR = 1.00, 95% CI = 0.89 to 1.15). However, screened individuals had lower odds of Duke stage D CRC (cOR = 0.68, 95% CI = 0.50 to 0.93). We estimate 435 fewer Duke D CRC by age 80 years in 100 000 people screened biennially between ages 60 and 74 years compared with an unscreened cohort.

Conclusion: The impact of colorectal screening on advanced CRC incidence suggests that the program will meet its aim of reducing mortality.

Figure 1.

Flowchart detailing total study population, exclusions, and total included in the analysis.

Figure 2.

Effect of screening on the odds ratio of colorectal cancer by time since last test. A) All stages, B) Duke B or worse, C) Duke C or worse, D) Duke D. CI = confidence interval; OR = odds ratio.

Figure 3.

Cumulative relative risk of colorectal cancer by time since last test and stage in unscreened individuals compared with those screened. Corrected for self-selection bias. A) All stages, B) Duke B or worse, C) Duke C or worse, D) Duke D.

Figure 4.

Cumulative rate of colorectal cancer per 100 000 in a hypothetical cohort of individuals aged 60 to 79 years among screened individuals and the general population. Corrected for self-selection bias. A) All stages and B) for Duke stage D.