Metaplastic breast tumors with a dominant fibromatosis-like phenotype havea high risk of local recurrence

BACKGROUND. In the current study the authors describe the clinicopathologic characteristics of a low grade variant of spindle cell metaplastic tumors of the breast. Previously these tumors have been considered within a larger group recognized as metaplastic carcinoma, including cases with higher gra de features. METHODS. Breast tumors comprised predominantly of low grade spindle cells, with sparse low grade epithelial elements, were selected. Clinical features as well as macroscopic, microscopic, and immunohistochemical findings were reviewed with emphasis on the biologic behavior and the differential diagn osis from other spindle cell lesions. RESULTS. Of 30 tumors fulfilling strict criteria, 20 contained squamous or glandular elements associated with the spindle cells. Ten tumors were compr ised entirely of low grade spindle cells with limited clustered epithelioid cells. At the periphery, all tumors showed a proliferation of bland spindl e cells infiltrating the adjacent parenchyma and mimicking fibromatosis. Th e epithelioid cells and some spindle cells expressed both vimentin and one or more cytokeratins. Seven of eight patients treated by excisional biopsy developed local recurrence, whereas only one of ten patients treated with w ide excisional biopsy developed a local recurrence. No distant or regional metastases occurred. CONCLUSIONS. The presence of limited clusters of epithelioid cells along wi th a dominant fibromatosis-like pattern may be unique in the breast. The bi ologic potential of the fibromatosis-like, spindle cell, metaplastic breast tumors most likely is defined by their major histologic phenotype; they ar e capable of local recurrence with no demonstrated distant spread or region al metastases, as in pure fibromatosis of the breast. Cancer 1999;85:2170-8 2, (C) 1999 American Cancer Society.