Diagnostic Consideration of Spindle Cell Proliferations in the Breast

A 52-year-old woman with noninsulin dependent diabetes mellitus was found to have a 3.5-cm irregular spiculated right breast mass by mammography worrisome for malignancy. The patient underwent core needle biopsy followed by mastectomy and sentinel node biopsy. The pathologic examination of the breast mass revealed “fibromatosis-like” spindle cell carcinoma. The sentinel lymph node was negative for metastatic disease. This case illustrates the spindle cell variant of metaplastic carcinoma, which can be diagnostically challenging, especially in limited core biopsy material. Recent studies have highlighted the use of various immunohistochemical stains in the evaluation of spindle cell proliferations in the breast. We propose the use of several different keratin stains and the inclusion of p63 as part of the diagnostic workup of challenging spindle cell lesions of the breast.