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).
At high power of the same lesion, large epithelioid pleomorphic cells are seen spreading in a pagetoid fashion. These cells have light pink cytoplasm with ill-defined cell borders and pleomorphic nuclei with nucleoli. The cells were positive for CK7, CAM5.2, and negative for S100 (not shown).