Screening outcomes by risk factor and age: evidence from BreastScreen WA for discussions of risk‐stratified population screening

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.