RESUMEN
OBJECTIVES: To estimate rates of screen-detected and interval breast cancers, stratified by risk factor, to inform discussions of risk-stratified population screening. DESIGN: Retrospective population-based cohort study; analysis of routinely collected BreastScreen WA program clinical and administrative data. SETTING, PARTICIPANTS: All BreastScreen WA mammography screening episodes for women aged 40 years or more during 1 July 2007 - 30 June 2017. MAIN OUTCOME MEASURES: Cancer detection rate (CDR) and interval cancer rate (ICR), by risk factor. RESULTS: A total of 323 082 women were screened in 1 026 137 screening episodes (mean age, 58.5 years; SD, 8.6 years). The overall CDR was 68 (95% CI, 67-70) cancers per 10 000 screens, and the overall ICR was 9.7 (95% CI, 9.2-10.1) cancers per 10 000 women-years. Interactions between the effects on CDR of age group and five risk factors were statistically significant: personal history of breast cancer (P = 0.039), family history of breast cancer (P = 0.005), risk-relevant benign conditions (P = 0.012), hormone-replacement therapy (P = 0.002), and self-reported symptoms (P < 0.001). The influence of these risk factors (except personal history) increased with age. For ICR, only the interaction between age and hormone-replacement therapy was significant (P < 0.001), although weak interactions between age and family history of breast cancer or having dense breasts were noted (each P = 0.07). The influence of family history on ICR was significant only for women aged 40-49 years. CONCLUSIONS: Screening CDR and (for some risk factors) ICR were higher for women in some age groups with personal histories of breast cancer or risk-relevant benign breast conditions or first degree family history of breast cancer, women with dense breasts or self-reported breast-related symptoms, and women using hormone-replacement therapy. Our findings could inform the evaluation of risk-based screening.