Exploring Traditional Breast Cancer Risk Genes Among Aboriginal and Torres Strait Islander Women

Background: Germline pathogenic variants in BRCA1/2 increase breast and ovarian cancer risk, but their prevalence in Aboriginal and Torres Strait Islander (herein referred to as Aboriginal) families has never been studied. Consequently, their contribution to breast cancer in this population is unknown. Methods: This retrospective cohort study included 259 Aboriginal women and 789 age- and remoteness-matched non-Aboriginal women diagnosed with breast cancer (2001–2016). We assessed family history, genetic service referral and testing rates, and pathogenic variant rates in the context of testing access. Results: Family history data were available for more Aboriginal than non-Aboriginal cases (46% vs. 34%, p < 0.001), with no difference in reported first-degree relatives with breast (22.5% vs. 22.4%, p = 0.98) or ovarian cancer (4.2% vs. 2.2%, p = 0.29). Similar proportions were referred to genetic services for testing eligibility (5.4% vs. 7.2%, p = 0.392). Of those referred, similar proportions were offered testing (86% vs. 81%, p = 0.66). Across the full cohort, BRCA1/2 pathogenic variants were detected in 0.77% of Aboriginal versus 2.4% of non-Aboriginal women (p = 0.127); any pathogenic gene variant was detected in 0.77% versus 3.0% (p = 0.039). Conclusions: Pathogenic genetic variants were detected less frequently in Aboriginal women, although, in keeping with international clinical practice, most women diagnosed with breast cancer were not tested. Given that only a small proportion of the cohort underwent germline testing, this study cannot distinguish whether the lower detection rate reflects a genuinely lower population level prevalence of pathogenic variants or differences in historical referral, selection, and testing practices. These findings are hypothesis-generating and require validation in larger Australian Aboriginal studies including unselected populations with whole-population testing data.