Pigmented Plaque in the Axilla

C. Pigmented extramammary Paget disease

An incisional biopsy revealed an intraepidermal neoplasm consisting of pagetoid cells, characterized by a round, pale vacuolated cytoplasm and large pleomorphic nuclei. Immunohistochemical staining revealed that the lesion was positive for CK7, EMA, and surrounded by numerous reactive dendritic HMB-45–positive melanocytes scattered among the tumor cells (Figure, B-D). Based on these clinical and histologic manifestations, a diagnosis of pigmented extramammary Paget disease (EMPD) was formulated.

Extramammary Paget disease is an intraepithelial adenocarcinoma that most commonly involves the vulva but can also occur in the perianal skin, scrotum, penis, and axilla. It is sometimes associated with underlying adnexal or visceral cancer. Extramammary Paget disease usually manifests as dermatitis and/or eczematous lesions.¹ Occasionally, the lesion is pigmented. Pigmented EMPD is a very rare clinical-pathologic variant of EMPD. Although its clinical features are often indistinct and difficult to distinguish from other pigmented entities, appropriate histologic and immunohistochemical analysis is essential in securing a definitive diagnosis.