Spindle cell carcinoma of the breast, a mimicker of benign lesions: case report and review of the literature.

The clinical and pathologic features of a breast tumor with unusual morphology in a 69-year-old woman are presented. Spindle cell carcinoma is considered one of the variants of metaplastic carcinoma and is commonly described in the upper aerodigestive tract, but it is relatively rare in the breast. This case is uniquely different from the usual cases of spindle cell carcinoma because of the lack of squamous differentiation or a recognizable infiltrating ductal component at the light microscopic level. With immunohistochemical stains using keratin and actin, a rather prominent network of infiltrating compressed ductal structures became apparent. These immunohistochemical features are consistent with the current concept of myoepithelial origin for metaplastic carcinomas. Although mention has been made in the literature of cases in which this "bland" carcinoma could be confused with benign nonneoplastic conditions, few illustrated examples exist. The prognosis for this particular subgroup of metaplastic carcinoma may be somewhat better than that for ordinary ductal carcinoma. For prognostic purposes, this entity should be distinguished from other metaplastic carcinomas and sarcomas, but more importantly, it should be differentiated from lesions such as nodular fasciitis, reactive granulation tissue, and fibromatosis, with which it may be confused histologically.