Extramammary Paget Disease Secondary to Axillary Apocrine Carcinoma: Highlighting the Diagnostic Utility of a Limited Immunohistochemical Panel in a Resource-Limited Setting.

Extramammary Paget disease (EMPD) is a rare adenocarcinoma arising in apocrine gland-rich skin, most commonly affecting the genital and perianal regions, and may present as either a primary intraepidermal neoplasm or a secondary, epidermotropic extension of an underlying malignancy. We report the case of a 54-year-old Panamanian man who presented with a two-month history of a right axillary plaque, characterized by a beefy-red, moist surface with moderate scaling and scattered erosions, accompanied by intermittent burning pain and pruritus. Dermoscopy revealed milky-red areas interspersed with cloud-like, structureless areas, prompting a differential diagnosis that included Bowen disease, malignant melanoma, and EMPD. Histopathology demonstrated intraepidermal nests of large, pale cells with vesicular, pleomorphic nuclei; these cells were positive for epithelial membrane antigen, cytokeratin 7, and cytokeratin 8/18, and negative for S-100 and Melan-A. Wide local excision with lymph node dissection confirmed EMPD secondary to an underlying apocrine carcinoma. Axillary EMPD is uncommon and may be clinically subtle, leading to delayed diagnosis, particularly in resource-limited settings where access to immunohistochemistry (IHC) is restricted. Chronic erythematous or pruritic plaques on apocrine-rich skin should prompt biopsy, as histology, coupled with IHC, is essential for accurate classification and management. To our knowledge, this represents the first documented case of axillary EMPD reported in Panama.