Objectives Since the introduction of mammography, a greater extent of Ductal Carcinoma In Situ of the breast (DCIS) has been diagnosed. From a pathological and molecular view, DCIS cells have many similar characteristics of invasive cancer cells. Therefore, DCIS has been presumed to be a precursor of invasive breast cancers. However, treating these lesions does not seem to decrease the amount of invasive breast cancers. This has brought into question the potential of overdiagnosis as well as overtreatment. Women who have a diagnosis of DCIS only (a DCIS that does not progress to invasive cancer) may be receiving unnecessary aggressive treatments. Treatment trends of DCIS have not been examined for more than a decade in Australia and New Zealand. The aim of our study is to describe current temporal trends in the management of DCIS in Australian and New Zealand women.

Methods The BreastSurgANZ Quality Audit database captures data on the management and treatment of early and locally advanced breast cancer in Australia and New Zealand. Using this database, we conducted a descriptive study of the trends of management of women diagnosed with DCIS in Australia and New Zealand between the years of 2007–2016. In our study we looked at the surgical treatments, the adjuvant therapies, as well as the axillary surgeries conducted on women who only have a DCIS diagnosis. Additionally, we stratified these outcomes by age, menopausal status, histological grade and referral source.

Results There were 17883 women diagnosed with DCIS only in Australia and New Zealand from 2007–2016. We found that the treatment patterns for women diagnosed with DCIS were persistent over years, where no major changes in the management was observed. The most common type of surgery performed was breast-conserving surgery (66%), followed by mastectomy (37%). Sentinel node biopsy was conducted among 36%. Of women who were referred to the breast surgeons for symptomatic reasons 47% received a mastectomy, compared to 30% of the women who were referred by BreastScreen. Of women who were referred to the breast surgeons by BreastScreen 73% received Breast Conserving Surgery, compared to 54% who were referred for symptomatic reasons.

Conclusions We concluded that the practises performed on women diagnosed with DCIS in Australia and New Zealand between the years of 2007–2016, appear stable over time. However, further investigation is needed into exploring how well these treatment patterns are in accordance with current practice guidelines. In addition, we need to look at the results of the ongoing prospective studies, i.e. LORD, LORIS and COMET, investigating active surveillance for low-grade DCIS to understand if some of these women could be treated less aggressively. The outcomes of the treatment of DCIS with surgery are very good, however the need of this for all types of DCIS is uncertain.