A 75-year-old woman presented with a breast mass and underwent an excision (lumpectomy). The resultant specimen was referred to us for consultation. The specimen consisted of scattered mildly hyperplastic ducts embedded in a variably but generally hypocellular spindle cell stroma, as shown below.
At higher magnification (seen above), there were mild to scattered moderately pleomorphic cells, and scattered mitotic figures including apparently atypical forms could be identified. A broad spectrum cytokeratin cocktail (see below) showed strong positivity in the spindled cells.
An immunohistochemical stain for p63 (see below), was also positive in the spindle cell population, as well as in myoepithelial cells surrounding the intralesional benign ducts.
This is an example of a metaplastic carcinoma of the breast with a sarcomatoid phenotype in which an accompanying malignant glandular component is not present, at least in the available material. The sarcomatous elements in this case are relatively low grade and the term "spindle cell carcinoma" has been applied to similar tumors. Although metaplastic carcinomas as a group appear to have a relatively poor prognosis, the better differentiated lesions, such as the current case appear to fare better (though prognosis remains to be completely defined). As might be expected for a more stromal-like lesion, metastases to regional lymph nodes have been said to be less common, as opposed to hematogenous spread.
The take home message from this case is simply to not under diagnose the relatively bland and modestly cellular stroma as a benign process. I high index of suspicion, as well as a broad spectrum cytokeratin cocktail (not just AE1/AE3) and p63, should aid in the recognition of this neoplasm.