Abstract

Pigmented mammary Paget’s disease is rare with only a few cases reported since its original description. Clinically, it is often misdiagnosed as a melanocytic lesion due to its presentation as a pigmented skin lesion. We report a case of invasive ductal carcinoma of the breast presenting as a melanocytic skin lesion on the nipple. A 41-year-old woman presented with an itchy, bleeding lesion of the left breast nipple that had been persistent for seven months. Physical exam showed a 5 mm gray-black macule with irregular pigment globules, and shave biopsy was recommended to rule out an atypical nevus or melanoma. Histologic sections showed pagetoid cells and a glandular proliferation in the dermis with mild to moderate atypia. Pigment was present within the neoplastic cells. Immunohistochemical stains revealed that the tumor was positive for AE1/AE3, CK7, GATA3, ER, and E-cadherin, patchy positive for mammaglobin, and had loss of myoepithelial cell layer (CK5/6, p63, SMM, and calponin negative), consistent with invasive ductal carcinoma of the breast. D2-40 and p63 were negative, ruling out a primary adnexal tumor. SOX10 and MART-1 revealed colonization of the tumor cells by melanocytes. Azzopardi and Eusebi made the first description of hyperpigmented skin lesions resulting from underlying breast carcinoma in 1977. They hypothesized that involvement of the dermo-epidermal junction induced intraepidermal melanocytic proliferation and consequent pigmentation of the lesion. It is important to recognize this phenomenon, as clinically and histologically, skin lesions can mimic melanocytic lesions, and most importantly melanoma.

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