Risk factors for interval breast cancer: insights from a decade of a mammography screening program.

Purpose: Breast cancer remains a major global health issue, with mammography screening programs (MSPs) being critical for early detection to improve survival. Interval breast cancers (IBC) are an important quality criterion and have been linked with increased mortality. We aimed to identify risk factors for IBC diagnoses, based on MSP data.

Methods: In this retrospective cohort study, we merged data from the Swiss MSP "donna" with data from cancer registries from 2010 to 2019 to categorize cases as IBC or screen-detected breast cancer (SBC). We compared the incidence, tumor characteristics, and survival proportions of women with IBC versus SBC. We used a multivariable Poisson regression with robust errors to identify risk factors for IBC diagnoses.

Results: We identified 1134 breast cancer cases, specifically 251 IBC and 883 SBC. The 7-year survival proportions significantly deviated with 92.9% for women with IBC and 96.4% for women with SBC (p < 0.05). Women with IBC are diagnosed with significantly higher tumor stages (p < 0.05) and have a worse tumor biology in multiple dimensions e.g. larger tumor size or more often triple negative (p < 0.05). Higher breast density (BI-RADS d risk ratio (RR): 3.293), certain age groups (55-59 years RR: 1.345), and a family breast cancer history (RR: 1.299) were identified as significant (p < 0.05) risk factors for IBC diagnoses.

Conclusions: Women with IBC had lower overall survival proportions than women with SBC, possibly due to higher stages at diagnosis. Increased breast density and a positive family history of breast cancer could encourage MSPs to personalize their screening process (e.g. additional diagnostics).