Adherence to breast screening guidelines and breast cancer mortality: a population cohort study.

Background: Population-based breast screening programs diagnose cancers at earlier stage when they are easier to treat. Indeed, individuals screened as part of the Ontario Breast Screening Program (OBSP) are diagnosed with a lower stage of breast cancer than those who have never been screened. We sought to determine if adherence to OBSP guidelines is associated with differences in the rate of death from breast cancer in addition to cancer stage at diagnosis.

Methods: 48,927 women ≥ 51 years diagnosed with a first primary breast cancer in Ontario 2010-2017 were included and classified as an adherent screener, partial screener, or non-screener. The cohort was developed using administrative health databases linked by Ontario Health. Cause-specific hazard ratios (HR) and 95% confidence intervals (CI) were used to examine the association between adherence to OBSP guidelines and the rate of breast cancer death adjusting for age, rurality, and history of a prior cancer diagnosis. Death from non-breast cancer causes was considered a competing risk.

Results: Compared to adherent screenings, non-screeners and non-adherent screeners had higher rates of death from breast cancer (HR: 3.59, 95% CI 3.30-3.90 and HR: 1.69, 95% CI 1.47-1.95 respectively). Further, non-adherent screeners (i.e., screened ≥ once) had a lower rate of breast cancer death than non-screeners (HR: 0.47, 95% CI 0.41-0.54).

Interpretation: Individuals screened in the OBSP have a lower rate of death from breast cancer than non-screeners, even if they are not meeting screening guidelines. These findings suggest women should be encouraged to participate in breast screening regardless of their frequency of use.