External Validation of Four Breast Cancer Risk Models With and Without Breast Density in a prospective Dutch Screening Cohort
Author Block: J. Peters1, D. Van Der Waal1, M. Schmidt2, C. Van Gils3, M. Broeders1; 1Nijmegen/NL, 2Amsterdam/NL, 3Utrecht/NL
Purpose: Tailoring breast cancer screening to individual risk can improve its harm–benefit ratio versus a ‘one-size-fits-all’ approach. We externally validated four widely used risk models—Gail, BCSC, BOADICEA, and IBIS—in a large Dutch screening cohort. Recent model updates include breast density using different approaches (categorical or continuous), so we evaluated performance with and without density.
Methods or Background: The PRISMA study is a prospective cohort (2014–2019) embedded in the Dutch biennial breast cancer screening program, which invites women aged 50-75 years. Breast cancer risk was predicted for 38,767 participants using four models (Gail, BCSC, BOADICEA, IBIS) based on questionnaire data (personal, lifestyle, hormonal, family history) and breast density. Gail does not include density; BCSC uses density categories; BOADICEA and IBIS allow categories, a continuous measure, or no density. Volumetric percent density and Volpara Density Grades (Volpara version 1.5.0) were measured on raw mammograms. Breast cancers were ascertained via linkage with the Netherlands Cancer Registry until October 2023. Model performance for 5-year risk was evaluated using the concordance index (C-index), observed–expected (O/E) ratio, and calibration slope.
Results or Findings: During a median 4.3 years follow-up, 609 breast cancers occurred. Discrimination was poor for Gail (C-index 0.56) and modest for BCSC, BOADICEA and IBIS (C-indices 0.60-0.61). Calibration was good for BCSC (O/E 1.03, slope 0.81) and BOADICEA (O/E 0.96, slope 0.78), but IBIS (O/E 0.71, slope 0.66) and Gail (O/E 0.79, slope 0.59) overpredicted risk. Adding continuous breast density improved discrimination (ΔC-index +0.02–0.04) and calibration most.
Conclusion: Traditional breast cancer risk models show at most moderate performance; despite small improvements from continuous breast density, overall accuracy remains limited for personalized screening.
Limitations: The limitations of the study are incomplete family history and genetic data, which may particularly underestimate BOADICEA and IBIS performance.
Funding for this study: Dutch Cancer Society (KWF7626) and Dutch Research Society (ZonMw 200500004)
Has your study been approved by an ethics committee? Yes
Ethics committee - additional information: CMO Arnhem-Nijmegen reference no. 2014/177