Article|Articles in Press, 100820

Validation of the International Breast Cancer Intervention Study (IBIS) Model in the High Risk Ontario Breast Screening Program: A Retrospective Cohort Study

Open AccessPublished:March 12, 2023DOI:
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      Women with a remaining lifetime risk of breast cancer ≥25%, estimated using the International Breast Cancer Intervention Study (IBIS) model, are eligible for the High Risk Ontario Breast Screening Program (OBSP). This study examined the performance of IBIS 10-year risk estimates in the Program.


      This retrospective study included 7487 women aged 30–69 years referred to the High Risk OBSP between July 1, 2011, and December 31, 2016, with follow-up until December 31, 2018. Model calibration and discrimination were assessed. Analyses were conducted overall and stratified by age (< or ≥50 years). Different 10-year risk thresholds were compared to the current eligibility criteria.


      Overall, IBIS over-estimated the risk of breast cancer with an E/O ratio of 1.17, 95% CI 1.04, 1.35. Over-estimation was highest in women ages 50–69 years (E/O=1.29, 95% CI 1.03, 1.69), and for those in the top quartile of risk. Overall discrimination was fair with a c-statistic of 0.66 (95% CI 0.63, 0.70). Further, when using different 10-year risk eligibility thresholds most cases would have been missed in the 30–49 age group using the 8% 10-year risk threshold, while relatively few women aged 50–69 would have been ineligible at any of the thresholds examined.


      We found IBIS over-estimates the risk of breast cancer in this screening cohort but has adequate discrimination. Age-specific risk thresholds should be considered to optimize Program eligibility criteria.