In Focus: Mammary Paget’s Disease

A 52-year-old female presented with a well-defined, erythematous, crusted plaque over her left breast for two years. The plaque started as a small, erythematous papule over the areolar area of her left breast and slowly enlarged, extending over the nipple. The left nipple slowly became flattened as the lesion grew and formed a scaling crust (see Figure 1). The patient experienced occasional pain and tingling over the plaque. No underlying mass was detected on clinical examination or on subsequent ultrasound and mammography.

Histopathological examination showed acanthosis without any parakeratosis. There were nests of large, round, pale-staining cells with large, irregular nuclei and prominent nucleoli in the epidermis (see Figure 2). No underlying malignancy was noted. The cells were positive for CK7, CAM 5.2, and HER2, but negative for HMB 45 and CK 5/6. This constellation of clinical and histological features prompted a diagnosis of Paget’s disease of the breast.

First described by James Paget in 1874, Paget’s disease of the breast is a malignant disease that presents itself as an eroding, bleeding ulcer or eczematous lesion of the nipple (1). Paget’s disease is often associated with primary invasive or in situ carcinoma of the breast. Due to clinical overlap with chronic eczematous dermatitis, underdiagnosis or misdiagnosis causes a median delay of six months in starting the proper treatment (2). Treatment and prognosis depend on the presence and invasiveness of underlying malignancy.