Independent and Incremental Value of Breast Mass Orientation Angle in Ultrasound-Based Malignancy Prediction

Orientation of breast masses on ultrasonography is a well-recognized feature for differentiating benign from malignant lesions. Recent studies suggest that quantitative assessment of the orientation angle may improve diagnostic discrimination. This study aimed to evaluate the diagnostic performance of the orientation angle in a real-world cohort and to determine its incremental value when integrated with established clinical and sonographic predictors.

This retrospective study included 502 biopsy-proven breast lesions evaluated with ultrasound between 2019 and 2025. The orientation angle was defined as the acute angle between the longest axis of the lesion and the skin surface measured on transverse images. Inter-reader reliability was assessed using intraclass correlation coefficients (ICCs). Diagnostic performance was evaluated using receiver operating characteristic (ROC) analysis. Multivariable logistic regression models were constructed with and without the orientation angle to assess independent predictors of malignancy and incremental model performance.

Of the 502 lesions, 258 (51.4%) were malignant. Measurement reliability was excellent, with ICC values exceeding 0.96. Malignant lesions demonstrated significantly larger orientation angles than benign lesions and showed a stepwise increase across Breast Imaging Reporting and Data System categories. An optimal cut-off value of 25.3° yielded an AUC of 0.72, specificity of 90.2%, and a positive likelihood ratio of 4.66. In multivariable analysis, orientation angle remained independently associated with malignancy (odds ratio 1.03 per degree increase; p < .001).

Quantitative orientation angle is a reproducible and independent predictor of breast malignancy and provides incremental diagnostic value beyond conventional ultrasound descriptors, supporting its role as a complementary imaging biomarker in breast ultrasound assessment.