Immunohistochemical localization of S-100 protein in benign and malignant lesions of the breast

Immunohistochemical identification of S-100 protein using monoclonal antibody with peroxidase antiperoxidase technique was performed on 40 specimens of benign and malignant breast lesions. S-100 was expressed in 19 cases [47.5%] with a higher incidence in medullary carcinoma [87.5%]. S-100 immunoreactivity was considered as a marker for myoepithelial cells and used to distinguish between benign and malignant lesions. The discrepancy of staining results with antibody to S-100 protein can be explained by methods of fixation and immunohistochemical techniques used