Immunocytochemical investigation of intermediate filament proteins and epithelial membrane antigen in spindle cell tumours of the breast.

Seven consecutive cases of primary spindle celled tumours of the breast have been studied immunohistologically using antisera to the intermediate filament proteins (IFP) vimentin, cytokeratin, and desmin, and with an antibody to epithelial membrane antigen. Representative paraffin sections were examined using a peroxidase-antiperoxidase method. In three cases, very occasional foci of epithelial differentiation were apparent by conventional microscopy, and in one case, adjacent ductal carcinoma in situ was present. The remaining three cases were composed of spindle cell elements entirely, with no evidence of epithelial differentiation morphologically. Immunoreactivity of spindle cell elements for vimentin was found in all seven cases, and for cytokeratin in six cases. One case showed immunoreactivity for vimentin, cytokeratin, and desmin, and one case only for vimentin. Epithelial membrane antigen was not identified in the spindle cell elements of any tumour, but was present in the invasive epithelial component of three cases and the in situ component of one case. We conclude that many spindle cell tumours of breast show immunohistological evidence of epithelial differentiation and can be regarded as spindle cell carcinomas. However, in some cases IFP expression may be complex and histogenesis cannot be determined. This technique can aid histological diagnosis in some cases.