Abstract

A 74-year-old woman with no known history of malignancy presented with an asymptomatic solitary pink plaque on her left upper forehead of 12-months duration. The initial clinical differential diagnosis included cutaneous lupus erythematosus and annular lichen planus. Several skin biopsies were obtained and demonstrated a proliferation of epithelioid cells, arranged as single cells and nests, within the epidermis. These atypical cells possessed abundant pale to foamy cytoplasm, large nuclei with open chromatin, and small nucleoli. Follicular extension and mitotic figures were noted, but no definitive dermal invasion was identified. The pagetoid cells were positive for cytokeratin 7, androgen receptor, CEA, and EMA, but negative for PAS, Alcian blue, CK5/6, p40, MART-1, SOX10, CK20, ER, and PR. Patient had no concurrent malignancy detected. Given the clinical and histopathologic findings, a diagnosis of ectopic extramammary Paget’s disease (E-EMPD), was rendered. E-EMPD is defined by the occurrence of Paget’s disease in areas devoid of apocrine glands. E-EMPD is extremely rare, with only a few cases reported in the literature. Of these reported cases, the vast majority involved the trunk, whereas the remaining cases involved the scalp, nose, and neck. We report the first case of ectopic extramammary Paget’s disease presenting on the forehead. Our case highlights the significance of maintaining a high clinical index of suspicion, differentiating this entity from other diagnoses that can present with pagetoid spread histologically, and correctly interpreting the complex pattern of stains required to confirm a diagnosis of ectopic extramammary Paget’s disease.

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