Differentiation of Benign and Malignant BI-RADS 4–5 Breast Lesions Using Ultrasound Localization Microscopy–Derived Microvascular Biomarkers: A Prospective Study

Objective: To investigate qualitative and quantitative microvascular biomarkers derived from ultrasound localization microscopy (ULM) for differentiating benign and malignant breast lesions, and to evaluate their added value in improving BI-RADS-based diagnosis. Methods: In this prospective study, 295 patients with 301 breast lesions classified as BI-RADS category 4– 5 on conventional ultrasound (US) underwent contrast-enhanced ultrasound and ULM prior to surgery or biopsy. Qualitative vascular biomarkers and quantitative parameters were derived from ULM images. Diagnostic performance was evaluated using receiver operating characteristic (ROC) analysis. BI-RADS categories were further re-evaluated by integrating ULM-derived biomarkers. Results: ULM qualitative vascular biomarkers classified microvascular morphology into five patterns: avascular, dot-strip, circular, chaotic, and radial. Benign lesions predominantly exhibited avascular, dot-strip, and circular patterns (5.6%, 23.4%, and 48.6%, respectively), whereas malignant lesions were mainly characterized by chaotic and radial patterns (56.7% and 28.4%, respectively; p < 0.001). The qualitative assessment achieved an AUC of 0.825 (95% CI: 0.780– 0.871). All ULM quantitative biomarkers showed significant differences between benign and malignant lesions (all p < 0.05), among which maximum diameter demonstrated the highest diagnostic value (AUC = 0.898, 95% CI: 0.861– 0.935). A combined quantitative biomarker (CQB) model further improved performance (AUC = 0.920). Integration of ULM qualitative and quantitative biomarkers with BI-RADS further improved diagnostic accuracy (AUC = 0.976; sensitivity 0.964; specificity 0.916) and may improve risk stratification beyond BI-RADS. Conclusion: ULM-derived qualitative and quantitative microvascular biomarkers provide complementary information beyond conventional ultrasound and may improve diagnostic performance and risk stratification in BI-RADS 4– 5 breast lesions, but their role in safely reducing unnecessary biopsies requires further clinical validation.