This 79-year-old woman had a history of breast carcinoma. She developed a 4 cm erythematous eczematous plaque on her left nipple. Paget disease has a distinctive appearance, with individual cells and small nests infiltrating through the epidermis often without a clear dermal component. Other entities with pagetoid growth include Bowen disease, melanoma in situ, and adnexal carcinomas. Immunohistochemistry can be helpful in difficult cases. This case was positive for CK7 and CAM5.2, and negative for S100 (not shown).
Histologic sections of skin show a proliferation of pleomorphic epithelioid cells, confined to the epidermis. The infiltrate migrates in a pagetoid pattern, involving all levels of the epidermis. There is a moderate inflammatory infiltrate at the base.