Squamous cell carcinoma of the breast: a clinicopathologic analysis of eight cases and review of the literature.

Malignant neoplasms of the female breast composed of squamous cells are rare and constitute a particularly poorly understood facet of breast disease. Two pure squamous cell carcinomas ( SCCs ) of the breast and six tumors that displayed various combinations of malignant squamous elements and ductal breast adenocarcinoma were identified. Electron microscopy confirmed the diagnosis of SCC in two cases by the demonstration of regularly spaced desmosomes, tonofilament bundles, and keratohyaline granules. A review of the literature indicated that breast cancers with components of SCC are histologically variable. Approximately 30 cases of pure SCC and 80 cases of mixed adenocarcinoma and SCC (adeno-SCC) have been reported. Some of these squamous epithelium-containing tumors have displayed areas of cyst formation, spindle cell metaplasia, and pseudosarcomatous desmoplastic response, or origins in preexisting breast lesions, such as cystosarcoma phyllodes or dermoid cysts. Although this variability indicates a heterogeneous group of neoplasms, the overall prognosis for carcinomas of the breast with malignant squamous elements appears to be quite similar to that for ordinary breast adenocarcinomas of similar size and stage.