Clinical relevance of the SOUND and INSEMA trials in women with early breast cancer in Australia and New Zealand

Background: Axillary surgery in breast cancer has undergone progressive de-escalation. The recent Sentinel Node versus Observation after Axillary Ultrasound (SOUND) and Intergroup Sentinel Mamma (INSEMA) trials have demonstrated that sentinel lymph node biopsy may be safely omitted in selected patients. This study aimed to evaluate the clinical relevance and applicability of the SOUND and INSEMA trial criteria within the Australian and New Zealand context. Methods: Prospectively maintained data from the BreastSurgANZ Quality Audit (BQA) was analysed. Patients with invasive breast cancer treated between 2019 and 2023 who met the inclusion criteria of the SOUND and INSEMA trials were identified. Results: A total of 69 122 patients were treated for invasive breast cancer over the five-year study period, of whom 30 822 fulfilled the inclusion criteria of either the SOUND or INSEMA trials. Overall, 34.0% and 44.6% of patients with invasive breast cancer in Australia and New Zealand met the SOUND and INSEMA eligibility criteria, respectively. Tumour characteristics of BQA patients were more closely aligned with those reported in the SOUND trial than the INSEMA trial, although key differences in other clinicopathological features were observed. Conclusions: The SOUND and INSEMA trial criteria are applicable to over one-third of patients with invasive breast cancer in Australia and New Zealand, supporting the potential relevance of axillary surgery de-escalation in this population.