Immunohistochemical study of mammary and extra‐mammary Paget's disease

Paraffin sections of 13 cases of Paget's disease (six mammary and seven extramammary) were investigated with mono‐ and polyclonal anti‐carcinoembryonic antigen (CEA) and with monoclonal anti‐human milk fat globule membrane antigen (HMFG). One of these cases was also analysed in cryostat sections with monoclonal anti‐cytokeratin and anti‐keratin. Three immunohistochemical labelling patterns were identified: (1) All six cases of mammary Paget's disease were positive for anti‐HMFG and negative with monoclonal anti‐CEA (although they stained to a variable degree with polyclonal anti‐CEA). (2) Two cases of extra‐mammary Paget's disease (both anal location) were positive with monoclonal anti‐CEA and only weakly stained for HMFG suggesting epidermal spread from a colo‐rectal carcinoma. (3) The other five cases of extra‐mammary Paget's disease were negative or weakly stained for CEA and positive for HMFG. We speculate that this group of cases represents epidermotropic eccrine carcinoma. The immunohistochemical use of monoclonal anti‐HMFG and ‐CEA is helpful in the diagnosis of Paget's disease; moreover it gives information about the origin of the primary tumour.