Low-grade fibromatosis-like spindle cell carcinoma of the breast.

Low-grade fibromatosis-like spindle cell carcinoma is a rare tumor in the breast, and represents a variant of the very heterogeneous group of metaplastic carcinomas of the breast. These tumors warrant distinction because of their resemblance to pure fibromatosis, their propensity for local recurrence, and their favorable prognosis among the metaplastic carcinomas of the breast. The diagnosis is potentially challenging, particularly on core needle biopsies, because of the morphologic overlap with other low-grade spindle cell lesions. Recognition of a proliferation of cytologically bland spindle cells with areas of epithelial differentiation in combination with immunohistochemistry using antibodies against cytokeratins and myoepithelial markers should aid in producing a definitive diagnosis. These tumors can be locally aggressive with an increased incidence of local recurrence, but the potential for lymph node or distant metastasis is low. Complete excision with adequate margins is considered curative in the majority of cases.