Factors Predictive of Treatment by Australian Breast Surgeons of Invasive Female Breast Cancer by Mastectomy rather than Breast Conserving Surgery

Background: The National Breast Cancer Audit Database of the Society of Breast Surgeons of Australia and New Zealand is used by surgeons to monitor treatment quality and for research. About 60% of early invasive female breast cancers in Australia are recorded. The objectives of this study are: (1) to investigate associations of socio-demographic, health-system and clinical characteristics with treatment of invasive female breast cancer by 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 surgery type for cancers diagnosed in 1998-2010. Results: Of 30,299 invasive cases analysed, 11,729 (39%) were treated by mastectomy 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 mastectomy was 1.03 (0.99, 1.07) for women from inner regional areas and 1.05 (1.01, 1.10) for those from more remote areas. 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 in multiple logistic regression analysis. Conclusions: Results confirm previous studies showing higher mastectomy rates for residents of more remote areas, those treated by surgeons with low case loads, and those with large cancers. Reasons require further study, including possible effects of surgeon and woman's choice and access to radiotherapy services.