Aboriginal and Torres Strait Islander Females and Survival from Breast Cancer.

Background: Despite access to universal health care, Aboriginal and Torres Strait Islander females (hereafter respectfully referred to as Aboriginal) in Australia have higher breast cancer incidence and mortality rates. We investigated the factors contributing to these survival disparities.

Methods: Aboriginal females (n = 395; 0.7%) and non-Aboriginal females (n = 57,618; 99.3%) with breast cancer were identified from Victoria, Australia. Clinical, pathologic, demographic, and socioeconomic variables were analyzed. Endpoints were all-cause and breast cancer-specific mortality. HRs were estimated using Cox regression. Stromal tumor-infiltrating lymphocytes were evaluated from a subset of Aboriginal females and compared with females in The Cancer Genome Atlas.

Results: Registry data revealed that Aboriginal females were younger (P < 0.001), had more advanced stage disease (P = 0.007), and were more likely to live in nonmetropolitan areas (P < 0.001) and in areas of greater disadvantage (P < 0.001) compared with other females at diagnosis. Age-adjusted multivariate analysis revealed a higher all-cause mortality risk (HR 1.27; 95% confidence interval, 1-1.61) for Aboriginal females, but this risk diminished for breast cancer-specific mortality and after adjustment for stage and grade. Breast cancers from Aboriginal females had significantly reduced stromal tumor-infiltrating lymphocytes in the luminal and triple-negative subtypes compared with The Cancer Genome Atlas.

Conclusions: Mortality for females with breast cancer was influenced by socioeconomic, geographic, and clinical factors. Notably, Aboriginal females with tumor features typically associated with favorable outcomes experienced poorer outcomes. The reduced immune infiltrate warrants further investigation.

Impact: These findings highlight the need to address socioeconomic inequities and ensure culturally safe cancer care. Further research should explore biological and environmental factors influencing outcomes for Australian Aboriginal females.