Mammary and extramammary Paget's disease

Mammary and extramammary Paget's disease are uncommon intraepithelial adeno carcinomas. Both conditions have similar clinical features, which mimic inf lammatory and infective diseases. Histological diagnostic confusion can ari se between Paget's disease and other neoplastic conditions affecting the sk in, with the most common differential diagnoses being malignant melanoma an d atypical squamous disease. The glandular differentiation of both mammary Paget's disease and extramammary Paget's disease is indicated by morphologi cal appearances, the presence of intracellular mucin in many cases, and pos itive immunohistochemical staining for glandular cytokeratins, epithelial m embrane antigen, and carcinoembryonic antigen. This article provides an ove rview of mammary and extramammary Paget's disease and discusses recent evid ence regarding the cell of origin. The concepts of primary and secondary Pa get's disease are presented and the differential diagnosis is discussed wit h reference to immunohistochemical markers that might be of diagnostic valu e.