The effect on colorectal cancer incidence and staging with population-based FOBT-screening in Sweden

To investigate colorectal cancer (CRC) incidence and stage of disease in the population invited vs. not invited to the guaiac-based Fecal Occult Blood (gFOBT) and Fecal Immunochemical Test (FIT) colorectal cancer screening program in Stockholm-Gotland, Sweden, 2008-2021, and to estimate the incidence rate by sex and localization in the colorectum.

The study cohort consisted of all 60-69-years-old residents of the Stockholm-Gotland region 2008-2012 according to the population register. Screening with biennial gFOBT was successively implemented in the region by randomly inviting birth cohorts of the target group to different year of start of screening from 2008 and replaced by FIT with cut-off level 40 µg/g in women and 80 µg/g in men for a positive test in 2015. Record linkage was made to the National Cancer Register and to the Swedish Colorectal Cancer Register (SCRCR). The age-standardized CRC incidence ratio was compared in invited and non-invited during screening and in 70-75-year-olds and assessed overall and by sex, CRC stage and localization.

In total, 320,989 and 151,533 individuals were invited to a first screening and FIT round, and 5,972 CRCs were diagnosed. During screening, the overall age-adjusted incidence ratio for the gFOBT- and FIT-invited compared to the non-invited was 0.99 (95% CI 0.91-1.07) and 1.03 (95% CI 0.93-1.15), respectively. Post screening, 70-75 years of age, the overall incidence rate was 12% lower among the invited than the non-invited (RR 0.88, 95% CI 0.81-0.97). During FIT screening, the incidence for stage I and proximal CRC was 38 and 23% higher than in the non-invited (RR 1.38, 95% CI 1.09-1.76 and RR 1.23, 95% CI 1.02-1.48 respectively). The incidence post screening was 22% lower regarding stage I CRC, 13% lower in women, and 17% lower for distal CRCs as compared to the non-invited (RR 95% CI 0.78 0.63-0.95, 0.87 0.76-1.00 and 0.83 0.74-0.94 respectively).

In the Stockholm-Gotland program, the FIT screening significantly increased the incidence rate in early staged and proximal CRCs as compared to the uninvited, and the significant decrease in the overall CRC incidence post screening was mainly seen in distal, early staged CRCs in women.