Background. Racialized individuals are more likely to be diagnosed with breast cancer at younger ages and are less likely to utilize breast cancer screening resources. Prior literature has indicated that structural factors such as socioeconomic status, access to primary care, and knowledge about screening guidelines influence screening adherence.

Objective. The objective of this study was to understand the landscape of breast cancer screening participation in Ontario by neighborhood racialized and newcomer status among individuals eligible for the Ontario Breast Screening Program (OBSP) during the study period (i.e., ages 50-74) and those not eligible (i.e., under age 50 years).

Methods. Linked administrative health databases were used to identify two cohorts of individuals diagnosed with breast cancer between 2001 and 2023 in the province of Ontario, Canada. The first included individuals who were OBSP-eligible (n=120,041) and the second included individuals under 50 who were not eligible for the OBSP during the study period (n=37,498). The Ontario Marginalization Index (ON-Marg) is a tool that combines demographic indicators from census tract data to summarize four distinct domains of marginalization. The racialized and newcomer (R&N) populations domain (presented as quintiles) measures the proportion of newcomers and non-white, non-Indigenous populations in the neighbourhood where an individual is residing. Multinomial logistic regression was used to examine the relationship between R&N quintile and adherence to screening guidelines in the OBSP-eligible cohort. Individuals were classified as adherent (having a mammogram every two years through OBSP), non-adherent (screened but not according to guidelines), or never screened (no OBSP record). In the younger cohort, the effect of R&N quintile on the odds of ever having had a screening mammogram prior to diagnosis was examined using binomial logistic regression.

Results. Among individuals in the OBSP-eligible cohort in the highest R&N quintile (i.e., the most racialized), there was an increased odds of never (OR: 1.30, 95% CI: 1.24, 1.36) and non-adherent (OR: 1.25, 95% CI: 1.18, 1.32) screening, compared to adherent screening. This disparity was further augmented by income. Individuals in both the lowest income quintile, and the highest R&N quintile, were 79% more likely to have never been screened than those in the lowest R&N quintile (OR: 1.79 95% CI: 1.61, 1.99). In the under 50 cohort, almost half had a screening mammogram more than 6 months prior to diagnosis (outside of the OBSP). While the odds of having a mammogram did not differ by R&N quintile, individuals in the lowest income quintile were less likely to have had a screening mammogram compared to the highest income quintile (OR: 0.63, 95% CI: 0.59, 0.68).

Conclusion. This study identifies lower adherence to breast cancer screening guidelines among individuals living in highly racialized, lower income neighborhoods. These disparities are seen even within a publicly funded health-care system where screening comes at no cost to the patient. Work needs to be done to identify and reduce barriers to screening in these populations.