Abstract:Objecitve To investigate the clinicopathological characteristics, immunohistochemical expression, diagnosis and differential diagnosis of breast tumors with osteosarcoma differentiation. Methods HE and immunohistochemical staining were performed on 4 cases of malignant breast tumors with osteosarcoma differentiation in the First Affiliated Hospital of Guangxi University of Chinese Medicine.Clinical data were analyzed and the literature were reviewed. Results Among the 4 patients, 2 patients had malignant phyllodes tumor with osteosarcoma differentiation, 1 patient had metaplastic breast carcinomas with osteosarcoma differentiation, and 1 patient had papilloma with osteosarcoma differentiation.Immunohistochemistry:the components of osteosarcoma expressed Vimentin and P120, while the metaplastic carcinoma expressed CK-P, E-Cad, P120, CK14, CK34 and P63.The lobular tumor spindle mesenchymal cells expressed Vimentin, SMA, CD10, CD34, and CD117. Conclusion Breast osteosarcoma is usually one of the components of other types of tumors, and the diagnosis depends on pathology.It is highly malignant and mainly metastases to the bloodstream.Radical mastectomy is the main treatment measure, and chemotherapy or local radiotherapy may be effective in some cases.