Spindle cell carcinoma of the breast. A clinocopathologic and ultrastructural study.

The clinical and pathologic features in six cases of spindle cell carcinoma of the breast were reviewed. Histologically this tumor is characterized by sheets of spindle cells often containing squamous epithelial islands and numerous cystic spaces lined by epidermoid carcinoma or benign appearing squamous epithelium. Areas of transition from the squamous epithelium or epidermoid carcinoma to malignant spindle cells were seen in all cases. Features of squamous epithelial differentiation were found in the spindle areas of the one tumor examined by electron microscopy. The prognosis in this neoplasm is similar to that in the more common breast carcinomas. Spindle cell carcinoma therefore should be distinguished from fibrosarcoma, stromal sarcoma, and carcinosarcoma. Moreover, it should be separated from the broader category of "metaplastic carcinoma," since this term includes a heterogeneous group of tumors of uncertain histogenesis and prognosis.