Breast Cancer Characteristics and Outcomes in Canadian Black Women by Ancestry

Breast cancer is the most common cancer among women in Canada. Its presentation and outcomes vary significantly by race/ethnicity. This study explores breast cancer incidence, age at diagnosis, stage, subtype, and mortality, comparing Black and White women aged 20 years and older, using the 2011 and 2016 Canadian Census Health and Environment Cohorts databases. Black women were disaggregated into Caribbean, Central/West African (C/WA), Southern/East African (S/EA), and "Other" ancestry groups. The Black female study population had a lower mean age (43.0 years) than the White (50.5 years). Black women had lower overall age-standardized breast cancer incidence than White women. The age-specific incidence in Black women ages 30-39 of Caribbean origin was higher (RR 95% CL, 1.36, 1.04-1.79; 58.7 vs. 43.1 cases/100,000 person-years) than in White. White women had 14.6% of cases diagnosed at ages 20-49 compared to over 50% in Black women of C/WA and S/EA origins, with highest proportions of diagnoses occurring at least 10 years earlier among Black women (C/WA 46, S/EA 48, Caribbean 57, White 67). Proportions of prognostic stage I diagnoses were less common among Black vs. White women (53.2% vs. 65.9%, <i>p</i> < 0.0001), and triple negative breast cancer was more frequent among Black women (17.1% vs. 9.9%, <i>p</i> < 0.0001), particularly those of Central/West African ancestry (21.8%). Higher age-specific mortality was observed among Black women with Caribbean origins aged 40-49 (RR 95% CL, 1.70, 1.19-2.42) and 50-59 (RR 95% CL, 1.42, 1.08-1.88) compared to White women. Breast cancer characteristics and outcomes vary substantially by ancestry within Canada's Black population. Tailored screening strategies accounting for earlier onset and aggressive subtypes may help mitigate disparities.