Xueling Zhang ¹ Wu Shaoyou ² Xiao Zu ^1* Xiaojing Li ^3* 晴 张 ⁴ Yongzhen Ren ^4* Qian Xiaoqin ⁴ Shan Tong ^4* Hongbo Li ^1*

• ¹ Nanjing University of Chinese Medicine, Nanjing, China
• ² Shanghai University, Shanghai, China
• ³ Second Affiliated Hospital of Soochow University, Suzhou, Jiangsu Province, China
• ⁴ Jiangsu University Affiliated People's Hospital, Zhenjiang, Jiangsu Province, China

Purpose: Accurate preoperative identification of Human epidermal growth factor receptor 2 (HER2) low expression breast cancer (BC) is critical for clinical decision-making. Our aim was to use machine learning methods to develop and validate an ultrasound-based radiomics nomogram for predicting HER2-low expression in BC.: In this retrospective study, 222 patients (108 HER2-0 expression and 114 HER2-low expression) with BC were included. The enrolled patients were randomly divided into a training cohort and a test cohort with a ratio of 8:2. The tumor region of interest was manually delineated from ultrasound image, and radiomics features were subsequently extracted. The features underwent dimension reduction using the least absolute shrinkage and selection operator (LASSO) algorithm, and rad-score were calculated. Five machine learning algorithms were applied for training, and the algorithm demonstrating the best performance was selected to construct a radiomics (USR) model. Clinical risk factors were integrated with rad-score to construct the prediction model, and a nomogram was plotted. The performance of the nomogram was assessed using receiver operating characteristic curve and decision curve analysis. Results: A total of 480 radiomics features were extracted, out of which 11 were screened out. The majority of the extracted features were wavelet features. Subsequently, the USR model was established, and rad-scores were computed. The nomogram, incorporating rad-score, tumor shape, border, and microcalcification, achieved the best performance in both the training cohort (AUC 0.89; 95%CI 0.836-0.936) and the test cohort (AUC 0.84; 95%CI 0.722-0.958) , outperforming both the USR model and clinical model. The calibration curves showed satisfactory consistency, and DCA confirmed the clinical utility of the nomogram. Conclusion: The nomogram model based on ultrasound radiomics exhibited high prediction value for HER2-low BC.