RESUMO
Although mammary carcinoma is one of the most common malignancies among women, sarcoma taking origin from the breast tissue is extremely rare. Most of the mammary sarcomas represent a specific entity such as malignant phyllodes tumor, liposarcoma, or angiosarcoma. However, some cases do not fit into any specific category of sarcoma. These cases are diagnosed with breast sarcoma-not otherwise specified (NOS) type. They constantly express CD10 and are called as NOS type sarcoma with CD10 expression. Herein, we report a case of primary mammary sarcoma-NOS type with CD10 expression in an 80-year-old male. It was misdiagnosed with carcinoma breast on fine-needle aspiration. However, on histology, it was a high-grade tumor without any specific differentiation. Immunohistochemical results showed diffuse strong expression of vimentin and CD10, whereas pancytokeratin, desmin, and CD34 were negative. These tumors are considered a variant of sarcoma with myoepithelial differentiation.