Cytokeratin 7 staining in mammary and extramammary Paget's disease

There are a variety of routine and immunohistochemical stains used to diagnose mammary and extramammary Paget's disease (MPD and EMPD). Most of the stains commonly used, however, show a positive reaction in the Paget's cells in all cases. We wanted to assess which immunohistochemical stain is the best for the diagnosis of MPD and EMPD, as well as the best stain for identifying small foci of tumors in evaluating tumor margins. We evaluated nine cases of MPD and nine cases of EMPD, which were randomly chosen, with a battery of immunohistochemical stains. These stains included cytokeratin 7, cytokeratin 20, carcinoembryonic antigen, Ber-EP4, and CAM 5.2. Cytokeratin 7 was the only immunohistochemical stain that stained all of the cases diffusely, and, in all of the cases, the staining of the Paget's cell was intense and specific within the epidermis. We concluded that cytokeratin 7 is the immunohistochemical stain of choice in the diagnosis of Paget's disease. Because cytokeratin 7 seems to identify single cells, it might also be valuable in evaluating surgical margins for small foci in a tumor such as EMPD, which might have a multifocal origin.