【Abstract】 Objective To investigate the clinical and pathological characteristics of spindle cell / sarcoma of the breast, and to evaluate the expression and differential diagnosis of conventional ultrasound and contrastenhanced ultrasound.Methods 1 cases of breast spindle cell / sarcoma were treated with conventional ultrasound, contrastenhanced ultrasound, biopsy, surgical resection, pathological HE staining, immunohistochemistry test and review of the literature. Results The female patient was 62 years old. The mass was located between the right side of the mammary gland layer and pectoralis major muscle, conventional ultrasound showed a predominantly cystic echo mass that mixed cystic and solid, contrastenhanced ultrasound showed inhomogeneous high enhanced with irregular enhanced area. The tumor cells were mainly composed of spindle cells, random distribution, interspersed with a few new capillaries, and necrosis in tumor cells. Stromal smooth muscle cells and inflammatory cells infiltration were visible. Immunohistochemically, the tumor cells expressed vimentin, SMA, CK, but the tumor cells did not express CD34, CD56,S100, CK7, HCK, ER, PR, EMA, desmin, BCL2 and P36 . The proliferation index of the Ki67was 75%. Conclusion Spindle cell / sarcoma of the breastis is extremely rare. The mass is often huge and edge warping and associated with cystic degeneration. There is no obvious specificity of conventional ultrasound and contrastenhanced ultrasound. The diagnosis should be combined with histopathological and immunohistochemical detection.