Microscopic Description -- An 80 Year Old Woman with a Left Breast Mass


H & E slides show a tumor infiltrating the breast tissue with extension into the adjacent fat (Fig. 1). It consists predominantly of a spindle cell proliferation admixed with the scattered small irregular ducts. The spindle cells are arranged in a feathered pattern in some areas (Fig. 2) and show a more storiform distribution in others (Fig. 3). A few angioid areas mimicking a capillary network are identified (Fig. 4) and consist of flattened endothelial-like cells forming intersecting strands that mix with a collagenous stroma. The neoplasm is moderately cellular without appreciable pleomorphism of the spindle cell component, which shows rounded, plump or stellate nuclei subtly merging with fibroblasts and myofibroblasts and presenting a mitotic rate of 4 mitotic figures per 10 HPF. An inflammatory infiltrate predominantly composed of lymphocytes and plasma cells is present. Sparse areas of necrosis represented by focal ischemic, densely acellular collagen are present. The ducts are arranged in a hazard pattern throughout the spindle cell proliferation and in areas appear to merge with the spindle cells (Fig. 5, 6). A single layer of atypical epithelium lines the ducts. Occasional cords and small nests of atypical epithelium are noted. Immunoreactivity is summarized in table 1 and exemplified in Fig. 7 - CAM5.2, Fig. 8 - EMA, Fig. 9 - AE1/E3, Fig. 10 - Vimentin, and Fig. 11 - Actin.


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