Breast Screening and Breast Cancer Survival in Aboriginal and Torres Strait Islander Women of Australia

Aboriginal and Torres Strait Islander people comprise about 2.5% of the Australian population. Cancerregistry data indicate that their breast cancer survivals are lower than for other women but the completenessand accuracy of Indigenous descriptors on registries are uncertain. We followed women receiving mammographyscreening in BreastScreen to determine differences in screening experiences and survivals from breast cancerby Aboriginal and Torres Strait Islander status, as recorded by BreastScreen. This status is self-reported andused in BreastScreen accreditation, and is considered to be more accurate. The study included breast cancersdiagnosed during the period of screening and after leaving the screening program. Design: Least square regressionmodels were used to compare screening experiences and outcomes adjusted for age, geographic remoteness,socio-economic disadvantage, screening period and round during 1996-2005. Survival of breast cancer patientsfrom all causes and from breast cancer specifically was compared for the 1991-2006 diagnostic period usinglinked cancer-registry data. Cox proportional hazards regression was used to adjust for socio-demographicdifferences, screening period, and where available, tumour size, nodal status and proximity of diagnosis totime of screen.
Results: After adjustment for socio-demographic differences and screening period, Aboriginaland Torres Strait Islander women participated less frequently than other women in screening and re-screeningalthough this difference appeared to be diminishing; were less likely to attend post-screening assessment withinthe recommended 28 days if recalled for assessment; had an elevated ductal carcinoma in situ but not invasivecancer detection rate; had larger breast cancers; and were more likely than other women to be treated bymastectomy than complete local excision. Linked cancer registry data indicated that five-year year survivalsof breast cancer cases from all causes of death were 81% for Aboriginal and Torres Strait Islander women,compared with 90% for other women, and that the former had larger breast cancers that were more likely tohave nodal spread at diagnosis. After adjusting for socio-demographic factors, tumour size, nodal spread and timefrom last screen to diagnosis, Aboriginal and Torres Strait Islander women had approximately twice the risk ofdeath from breast cancer as other women.
Conclusions: Aboriginal and Torres Strait Islander women have lessfavourable screening experiences and those diagnosed with breast cancer (either during the screening period orafter leaving the screening program) have lower survivals that persist after adjustment for socio-demographicdifferences, tumour size and nodal status.