·To comparatively analyze features of metaplastic carcinoma of the breast (MBC) images and immunological characteristics.

·The data of 30 patients with MBC treated in Renji Hospital, Shanghai Jiao Tong University School of Medicine from January 2008 to January 2021 were analyzed retrospectively, and the imaging findings and immunohistochemical results of tumors were analyzed and compared.

·A total of 31 lesions were found in 30 cases of MBC, including 18 squamous cell carcinomas, 3 mixed metaplastic carcinomas, 7 mesenchymal differentiated carcinomas, 1 myoepithelial carcinoma, and 2 spindle cell carcinomas. All patients were female, aged from 33 to 89 years old, with an average age of (61.8±14.2) years. The maximum size of the tumors was 101.0 mm while the minimal was 6.6 mm, with the medium size 25.5 mm and the average size (33.1±18.5) mm. A total of 29 patients underwent ultrasound examination before operation, with a total of 30 lesions. Among them, 23 lesions were irregular-shaped (76.7%), 19 lesions were hypoechoic (63.3%), 11 lesions were mixed echogenicity (36.7%), 14 lesions were found with unclear boundary (46.7%), and 7 lesions were accompanied by small internal calcifications (23.3%). Five cases of axillary lymph nodes were found, in which 3 cases were confirmed by pathology as lymph node metastasis (10.3%). Eight patients were examined by computed radiography (CR), showing lobulated, lumpy or asymmetrical shape, with unclear boundary, and some of them were found with coarse, heterogeneous or fine sand-like calcification. Magnetic resonance imaging (MRI) showed low signal intensity on T1 weighted imaging (T1WI) and T2WI in 6 patients. After enhancement, uneven signal, obscure border, and lobulated shape were shown. The MRI images of 3 patients showed that there was the possibility of surrounding tissue invasion and axillary lymph node metastasis respectively, but ultrasound examination did not show that. Except the invasion of pectoralis major, which was confirmed by pathology, the other 2 cases were all false positive. Four cases accepted CR, MRI and ultrasound, 2 cases of small calcification were missed by MRI and 1 case of axillary lymph node was missed by ultrasound. Sixteen lesions were triple-negative (51.6%), estrogen receptor (ER)/progesterone receptor (PR) expression rate was 32.2% and the over-expression rate of human epidermal growth factor receptor 2 (HER2) was 25.8%.

·Ultrasound, MRI and CR can complement each other and improve the accuracy of diagnosing the malignant degree of MBC.