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Case Reports

Abstract

Extramammary Paget’s disease (EMPD) commonly develops on skin regions containing apocrine glands and rarely occur on non-apocrine bearing areas. We report a case of intraepidermal carcinoma, consistent with EMPD, located on the forearm. A 67-year-old male presented with a 1.5 cm, red, slightly crusted plaque on the left lateral forearm. Patient denied fever, weight loss or night sweats.  Past medical history was unremarkable. A punch biopsy of the left dorsal forearm was performed showing atypical cells forming clusters at all levels of the epidermis. Pagetoid upward scatter of atypical cells were identified, involving the stratum corneum. These cells were positive for both EMA and CK-MNF. The atypical cells also showed diffuse, light positivity for Ber-EP4. Some of the pagetoid cells showed focal staining of CK7, especially in the upward epidermal layers. CKC and CK20 staining was negative. Based on the tumor’s morphology and immunostaining profile, a diagnosis of extramammary Paget’s disease was rendered. This case demonstrates a rare but clinically significant finding of extramammary Paget’s disease occurring on non-apocrine populated skin. Identification of the histopathologic and immunohistochemical features of this intraepithelial tumor is important to enable further work up in order to determine ectopic or metastatic tumor origin.