Answer: Paget’s disease

Histology: The epidermis is essentially replaced by malignant cells with abundant pale cytoplasm and enlarged nuclei with prominent nucleoli. The overlying epidermis is focally ulcerated and has a fibrino-inflammatory exudate over it. Beneath the epidermis there is a dense chronic inflammatory infiltrate, and the base of the epidermis is irregular and jagged in this area. However, immunostains for high- molecular weight cytokeratins (cytokeratin 5/6) demonstrate an intact epithelial epidermis in these areas, arguing against there being dermal invasion.

Discussion: Toker cells are intraepidermal extensions of the lactiferous ducts, which are present in normal nipples, and these cells will label for Cytokeratin 7 and CAM 5.2, just like Paget cells. However, Toker cells are cytologically benign, and they will not label for HER-2/neu like Paget cells do. Malignant melanoma is extremely rare in the nipple and can be distinguished from Paget cells by the absence of cytokeratin immunoreactivity and presence of HMB-45 immunoreactivity. One should note that Paget cells may take up melanin pigment from the adjacent epidermis to mimic melanoma.