Identification of Risk Factors for Interval Breast Cancer in a Population-based Screening Program

Background Evidence is limited on how radiologist interpretation, patient age, breast density, and family history influence interval breast cancer (IBC) risk. Purpose To investigate risk factors for IBC in women enrolled in a biennial population-based mammography screening program in Taiwan. Materials and Methods This retrospective study included women who underwent mammography in a population-based breast cancer screening program in Taiwan between January 1, 2004, and December 31, 2018. Standard two-view digital mammograms were interpreted by board-certified radiologists using Breast Imaging Reporting and Data System criteria. Performance measures included recall rate (RR), cancer detection rate (CDR), and positive predictive value (PPV); radiologist audit scores were derived from RR and PPV 1. IBC was defined as cancer diagnosed after a negative screening result and before the next 2-year screening. Multivariable Poison and logistic regression models with random intercepts for radiologist-facility pairs were used to estimate adjusted relative risks and odds ratios with 95% CIs. Results A total of 2 881 405 women (mean age, 56.1 years ± 6.6 [SD]; range, 45-69 years) underwent 6 592 768 mammographic examinations; 10 944 women were diagnosed with IBC. IBC risk per 1000 person-years was higher in women with a family history of breast cancer than in those without (1.41 [95% CI: 1.33, 1.51] vs 0.77 [95% CI: 0.75, 0.80]; P < .001) and in women with extremely dense breasts compared with those in lower breast density categories (1.15 vs 0.88, 0.54, and 0.29; P < .001). Women whose mammograms were interpreted by a radiologist with an audit score of 0-4 had fewer IBCs than those whose mammograms were interpreted by a radiologist with an audit score of 5 or greater (0.78 vs 1.23 per 1000 person-years; P < .001). Women whose mammograms were interpreted by a radiologist with low RR and CDR had the highest proportion of IBCs among all cancers detected (53.87% [95% CI: 49.71, 57.98]; P < .001). Among missed IBCs, asymmetry was the most common false-negative finding (22%). Conclusion High breast density, family history of breast cancer, and suboptimal radiologist performance were independently associated with increased IBC risk. These findings highlight the importance of performance auditing and targeted strategies to enhance early cancer detection in population screening. © RSNA, 2025 Supplemental material is available for this article.