Factors Predictive of Treatment by Australian Breast Surgeonsof Invasive Female Breast Cancer by Mastectomy rather thanBreast Conserving Surgery

Background: The National Breast Cancer Audit Database of the Society of Breast Surgeons of Australia andNew Zealand is used by surgeons to monitor treatment quality and for research. About 60% of early invasivefemale breast cancers in Australia are recorded. The objectives of this study are: (1) to investigate associationsof socio-demographic, health-system and clinical characteristics with treatment of invasive female breast cancerby mastectomy compared with breast conserving surgery; and (2) to consider service delivery implications.Materials and
Methods: Bi-variable and multivariable analyses of associations of characteristics with surgerytype for cancers diagnosed in 1998-2010.
Results: Of 30,299 invasive cases analysed, 11,729 (39%) were treated bymastectomy as opposed to breast conserving surgery. This proportion did not vary by diagnostic year (p>0.200).With major city residence as the reference category, the relative rate (95% confidence limits) of mastectomywas 1.03 (0.99, 1.07) for women from inner regional areas and 1.05 (1.01, 1.10) for those from more remoteareas. Low annual surgeon case load (≤10) was predictive of mastectomy, with a relative rate of 1.08 (1.03, 1.14)when compared with higher case loads. Tumour size was also predictive, with a relative rate of 1.05 (1.01, 1.10)for large cancers (40+ mm) compared with smaller cancers (<30 mm). These associations were confirmed inmultiple logistic regression analysis.
Conclusions: Results confirm previous studies showing higher mastectomyrates for residents of more remote areas, those treated by surgeons with low case loads, and those with largecancers. Reasons require further study, including possible effects of surgeon and woman’s choice and access toradiotherapy services.