Histopathological examination and immunohistochemical study. Detailed legend: (a) An extensive infiltrate with involvement largely concentrated in the deep epidermis. Epidermal hyperplasia and hyperkeratosis occurred to some degree (hematoxylin and eosin staining, original magnification ×40). (b) The tumor cells were large, with distinct borders, abundant pale cytoplasm, pleomorphic nuclei, and conspicuous nucleoli (hematoxylin and eosin staining, original magnification ×200). (c) Strong human epidermal growth factor receptor 2-positive membranous reactivity was detected in Paget’s cells in the epidermis (original magnification ×200). (d) Paget’s cells showing diffuse positivity for carcinoembryonic antigen (original magnification ×400). (e) Extramammary Paget’s disease manifested as cytokeratin-positive malignant cell epidermal infiltration (original magnification ×40). (f) Reactivity for gross cystic disease fluid protein of 15kDa (original magnification ×200).