Intraoperative specimen ultrasonography for margin assessment in breast conserving surgery in comparison with specimen mammography.

Introduction: Intra-operative specimen ultrasonography (IOUS) has been proposed as a cost-effective tool to assess surgical margins during breast-conserving surgery (BCS). We aimed to evaluate the diagnostic accuracy of IOUS in assessing radial margins in patients undergoing wide local excision (WLE) for non-palpable breast lesions and to compare its performance with specimen mammography (SM). Patients and Methods: This was a retrospective analysis of prospectively collected data from patients undergoing WLE for invasive breast cancer and mass-forming Ductal Carcinoma In Situ (DCIS) at a single tertiary referral centre between January 2018 and December 2022. The study protocol and outcomes were established prospectively in 2018, prior to commencement of data collection. All eligible patients undergoing intra-operative ultrasound (IOUS) and specimen mammography (SM) during the study period were prospectively identified, with exclusions subsequently applied according to the predefined eligibility criteria. Clinical, operative and imaging data were collected prospectively throughout the study period. All patients were operated by the same senior surgeon. Specimen ultrasound was performed intra-operatively by the operating surgeon. Radiological margins were considered clear when the distance from the tumour edge was >10 mm and close when ≤10 mm. When a close radiological margin was identified, an additional cavity shave was performed. IOUS findings were subsequently compared with the radiological margin assessment on specimen mammography and with final histopathological margin status. The primary outcome was the ability of IOUS and SM to identify radiologically close radial margins (≤10 mm), using final histopathological margin status as the reference standard. Results: 137 lesions (132 patients) were included in the study. The median age of patients was 66 (range: 33-86) years. 89 patients (67.5%) were screen detected. 126 (92%) lesions were invasive tumours. The median size of lesions on preoperative imaging was 15 (range: 5-18) mm. 548 radial margins were assessed, of which 22 (4%) were positive on histological analysis. IOUS demonstrated radiologically clear 517 margins (SM 513 margins) and radiologically close in 31 margins (SM in 35 margins). The sensitivity of IOUS was 68.2% (SM 72.7%) p = 0.61, and specificity 96.9%. (SM 96.4%) p = 1.0. IOUS had a negative predictive value of 98.6% (SM 98.8%). Conclusion: Intraoperative ultrasound demonstrates comparable diagnostic accuracy to specimen mammography for intra-operative margin assessment in non-palpable breast lesions. Its high specificity and negative predictive value support its reliability in excluding margin involvement. IOUS represents a rapid, accessible, and cost-effective alternative to SM, particularly in centres without specimen radiography or in resource-limited settings.