Multicenter ex vivo evaluation of an α-mannosidase–targeted fluorescent probe for intraoperative margin assessment in breast cancer

Determining an accurate intraoperative margin is essential in breast-conserving surgery (BCS) for breast cancer. This multicenter study assessed the diagnostic potential of a novel fluorescent probe targeting α-mannosidase, named the α-Man probe, in evaluating intraoperative margins. We analyzed 274 resected breast tissue samples, including malignant and benign lesions, across four institutions. Fluorescence intensity (FI) was measured 5 and 20 min following the application of the α-Man probe. Receiver operating characteristic analysis defined definitive thresholds for changes in FI (ΔFI), maintaining false positive and false negative rates at ≤ 3%. Diagnostic performance was also compared with a γ-glutamyltranspeptidase (GGT)-based fluorescent probe that we previously developed. Using 5-min ΔFI thresholds, positive, uncertain, and negative classifications were 24.1, 53.6, and 22.3%, respectively. At 20 min, these classifications improved to 28.1, 38.3, and 33.6%, respectively. At 5 and 20 min, positive predictive values were 93.9% and 94.8%, whereas negative predictive values were 95.1% and 96.7%, respectively. Compared with the GGT probe, α-Man substantially reduced the uncertain classification rate while maintaining high predictive accuracy. This study demonstrated that a two-step ΔFI-based protocol using the α-Man probe enables the accurate, real-time, and pathologist-independent assessment of resected specimens, supporting its future application to intraoperative margin evaluation during BCS.