Estimate of Proportional Incidence of Interval Colorectal Cancer

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European guidelines for colorectal cancer screening advise that the interval cancer rate be expressed as a proportion of the background incidence rate.

Innovative methods were used to estimate the proportional incidence of interval colorectal cancer (CRC) in an Italian cohort, and the results were found to be consistent with previous studies. The study results were published in Digestive and Liver Disease.1

To determine the crude and adjusted proportional incidence of interval CRC, Mancini and colleagues leveraged records from a regional Italian cancer registry that are linked to data from an ongoing fecal immunochemical test (FIT) screening program (2-year) for people aged 50 to 69 years, which was implemented in 2005. Interval CRC was defined as invasive CRC diagnosed within 2 years of a negative FIT.

A total of 790,885 negative FIT records from 280,090 participants were identified; after excluding records based upon eligibility criteria, including at least one follow-up evaluation, 434,295 records from 193,193 participants were included.

To correct for potential self-selection bias — an association between screening participation and the risk of disease — the crude proportional incidence was adjusted according to the cancer screening sensitivity as proposed by Hakama et al.2

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Data were accumulated for 198,302 person-years and 235,370 person-years for men and women, respectively. Interval CRC cases were identified in the registry. To estimate the crude proportional incidence, the observed number of interval CRC cases was divided by the expected number.

Among men, the proportional incidence of interval CRC was 0.06 (95% CI, 0.04-0.09) in the first year and 0.21 (95% CI: 0.16-0.26) in the second year. Among women, the proportional incidence of interval CRC was 0.17 (95% CI, 0.13-0.23) in the first year and 0.28 (95% CI, 0.22-0.36) in the second year.

A limitation of this research is that unlike previous studies of proportional incidence of interval CRC in Italy and other countries, this study adjusted for selection bias. In addition, the authors acknowledge that the records for cancer identification and classification may have contained inaccuracies.

The authors conclude, “In this study, innovative approaches to the estimate of proportional incidence of CRC were used. Both the adjusted and unadjusted figures were acceptable compared with the standards recommended by the Italian Group for Colorectal Cancer Screening.”

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1. Mancini S, Bucchi L, Giuliani O, et al. Proportional incidence of interval colorectal cancer in a large population-based faecal immunochemical test screening programme. Dig Liver Dis. 2020;0(0). doi:10.1016/j.dld.2020.02.007

2. Hakama M, Auvinen A, Day NE, et al. Sensitivity in cancer screening. J Med Screen. 2007;14:174-177. doi:10.1002/ijc.29053