# Breast Cancer Characteristics and Outcomes in Canadian Black Women by Ancestry

## TL;DR

Black women in Canada are more likely to be diagnosed with breast cancer at younger ages and with aggressive subtypes compared to White women, suggesting a need for tailored screening strategies.

## Contribution

The study reveals significant variations in breast cancer characteristics and outcomes among different Black ancestry groups in Canada, emphasizing the need for ancestry-specific approaches.

## Key findings

- Black women, especially those of Central/West and Southern/East African origins, are more likely to be diagnosed with breast cancer before age 50 compared to White women.
- Triple negative breast cancer is more common among Black women, particularly those of Central/West African ancestry.
- Black women with Caribbean origins experience higher age-specific mortality rates in their 40s and 50s compared to White women.

## Abstract

Breast cancer characteristics vary by race/ethnicity and ancestry in Canada. Using population-based census cohorts, this study compared Black and White women diagnosed with breast cancer aged 20 and older. Many Black women were diagnosed with breast cancer at younger ages, with over half of cases in Central/West and Southern/East African women occurring before age 50 compared to only one in seven cases in White women. Black women were more often diagnosed at stage II or higher and more commonly had triple negative breast cancer. The presence of the triple negative subtype was very high among Black women with Central/West African origins, consistent with patterns linked to West African genetic ancestry. Age-specific mortality was higher among Black women with Caribbean origins in their 40s and 50s. These findings highlight the substantial variation of breast cancer burden across Black ancestry groups in Canada and suggest that a greater awareness is needed and that earlier, tailored screening strategies may reduce disparities.

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%, p < 0.0001), and triple negative breast cancer was more frequent among Black women (17.1% vs. 9.9%, p < 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.