Breast screening and breast cancer survival in Aboriginal and Torres Strait Islander women of Australia

Abstract

Aboriginal and Torres Strait Islander people comprise about 2.5% of the Australian population. Cancer registry data indicate that their breast cancer survivals are lower than for other women but the completeness and accuracy of Indigenous descriptors on registries are uncertain. We followed women receiving mammography screening in BreastScreen to determine differences in screening experiences and survivals from breast cancer by Aboriginal and Torres Strait Islander status, as recorded by BreastScreen. This status is self-reported and used in BreastScreen accreditation, and is considered to be more accurate. The study included breast cancers diagnosed during the period of screening and after leaving the screening program. Design: Least square regression models 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 patients from all causes and from breast cancer specifically was compared for the 1991-2006 diagnostic period using linked cancer-registry data. Cox proportional hazards regression was used to adjust for socio-demographic differences, screening period, and where available, tumour size, nodal status and proximity of diagnosis to time of screen. Results: After adjustment for socio-demographic differences and screening period, Aboriginal and Torres Strait Islander women participated less frequently than other women in screening and re-screening although this difference appeared to be diminishing; were less likely to attend post-screening assessment within the recommended 28 days if recalled for assessment; had an elevated ductal carcinoma in situ but not invasive cancer detection rate; had larger breast cancers; and were more likely than other women to be treated by mastectomy than complete local excision. Linked cancer registry data indicated that five-year year survivals of 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 to have nodal spread at diagnosis. After adjusting for socio-demographic factors, tumour size, nodal spread and time from last screen to diagnosis, Aboriginal and Torres Strait Islander women had approximately twice the risk of death from breast cancer as other women. Conclusions: Aboriginal and Torres Strait Islander women have less favourable screening experiences and those diagnosed with breast cancer (either during the screening period or after leaving the screening program) have lower survivals that persist after adjustment for socio-demographic differences, tumour size and nodal status.