Integrating a small extracellular vesicle protein–based ovarian cancer score with O-RADS Ultrasound to improve preoperative risk stratification of adnexal masses.

5555 Background: Accurate preoperative differentiation of adnexal masses remains a major clinical challenge. Although the Ovarian-Adnexal Reporting and Data System (O-RADS) standardizes ultrasound-based risk assessment, approximately 30-35% of adnexal masses are classified as indeterminate (O-RADS 3/4), often resulting in diagnostic uncertainty, unnecessary surgery, or delayed referral to gynecologic oncologists. Conventional serum biomarkers such as CA125 are limited by poor specificity and biological heterogeneity. The small Extracellular vesicle (sEV)-associated biomarkers have emerged as a promising approach to improve diagnostic accuracy by more closely reflecting tumor-related molecular signals. This study evaluated whether a serum sEV-based Ovarian Cancer Score (OCS) provides independent and incremental diagnostic value when integrated with O-RADS ultrasound. Methods: This retrospective diagnostic study included 250 consecutive patients with adnexal masses treated at Sun Yat-sen Memorial Hospital. All patients underwent standardized transvaginal ultrasound with O-RADS classification and serum CA125 testing. OCS was assessed using a chemiluminescent immunoassay based on serum sEV-derived CA125, HE4, and C5a. Final histopathology served as the reference standard. Diagnostic performance was evaluated overall and stratified by O-RADS category. Univariate and multivariate logistic regression analyses were performed to identify independent predictors of malignancy. Results: Overall, OCS demonstrated significantly higher diagnostic accuracy for malignancy than serum CA125 alone. In masses with clearly benign or malignant imaging features (O-RADS 2 and 5), OCS maintained an accuracy of approximately 90% (87.5% and 94.6%). Within the clinically challenging O-RADS 3/4 subgroup (n = 115), OCS achieved a diagnostic accuracy of 86.1%, substantially outperforming serum CA125 (69.6%). Multivariate analysis identified OCS positivity as the strongest independent predictor of malignancy (OR 106.08, 95% CI 15.37-732.15, p < 0.001), exceeding individual high-risk ultrasound features such as ascites or mixed cystic-solid components. Diagnostic performance was further enhanced when OCS was combined with selected ultrasound characteristics. Conclusions: A serum sEV-based OCS provides robust and independent diagnostic information that complements O-RADS ultrasound in the preoperative evaluation of adnexal masses. By addressing the diagnostic gray zone of O-RADS 3/4, this integrated approach extends beyond conventional serum biomarkers and may support improved risk stratification and triage decisions. Clinical trial information: NCT06366997 .