Primary sarcoma of the breast is extremely rare and it is a diagnosis of exclusion, notably metaplastic carcinomas and malig-nant phyllodes tumors. We present a case of 53-year old Korean female with undifferentiated pleomorphic sarcoma with CD10 expression. It was a high grade tumor composed of spindle cells, and immunohistochemical analysis revealed negati- vity for cytokeratins and CD34, but focal positivity for actin, diffuse positivity for CD10 and vimentin. These results led to the diagnosis of undifferentiated pleomorphic sarcoma. This case represents a rare variant of primary breast sarcoma which imposes a diagnostic difficulty, and highlights the importance of CD10 expression.

Introduction
 Case report
 Discussion
 Acknowledgements
 References

• Ho Jong Jeon(Department of Pathology, Chosun University School of Medicine, Gwangju, Korea) Corresponding author
• Sung Chul Lim(Sung Chul Lim)
• Inju Cho(Department of Pathology, Chosun University School of Medicine)