574 The Incidence of ‘Negative’ Axillary Node Clearance Following Neoadjuvant Therapy, Its Potential Clinical Significance, and Recommendations: One Breast Unit Review of Practice

Aim To assess our unit’s approach in managing breast cancer patients with ‘negative’ axillary node clearance (ANC), following neoadjuvant systemic therapy (NST). ‘Negative’ ANC referred to scenarios where histologically proven metastasis were identified prior to treatment, but evidence of a positive node could not be found in the final surgical specimen. Method We retrospectively reviewed all ANCs performed in our unit over 8 months. Specifically, we focused on cases of ‘Negative ANC’. Each individual case was examined, reporting the incidence of ‘negative’ ANC and follow up investigations. Results Seventy ANCs were performed during the study period (September 2022 – April 2023). Notably, four cases, of which 3 patients had NST, were identified: indicating an incidence of 5.7%. Following surgery, each patient underwent numerous radiological investigations such as axillary ultrasound scans, CT chest, PET scans, over various timelines, ranging from 1 to 7 months post-surgery, to exclude the possibility of finding any residual node(s). Conclusions There was inconsistency in following-up these four patients with ‘negative ANC’. Although the possibility of achieving complete pathological response (pCR) existed, it was necessary to ensure all nodes within the axillary basin were retrieved, especially when post-NST nodal status is an important determinant of disease-free and overall survival. To address this oncological and histological concern, our unit will be clipping the biopsy proven node, prior to NST. This pre-NST localisation allows radiological assessment of the response during NST, providing an opportunity to de-escalate axilla surgery and re-evaluate the axilla in cases with ‘negative’ ANC outcomes.