Medullary carcinoma of the breast. Co-expression of keratin intermediate filaments and protein S-100 in tumor cells

We have chosen 10 medullary carcinomas from a retrospective investigation on 450 cases of breast carcinoma (2.2%), according to the histomorphological criteria of Ridolfi and colleagues. By immunoperoxidase staining, we have evaluated the distribution of keratin and vimentin intermediate filaments, of CEA and S-100 protein in cancer cells. A widespread positivity to keratins has been proved in 70% of medullary carcinomas. Numerous neoplastic cells have coexpressed S-100 protein. We hypothesize the epithelial and myoepithelial "intermediate" differentiation of keratin and S-100 protein positive tumour cells.