Ectopic hidradenoma papilliferum with apocrine differentiation: A case report and review of the literature

Hidradenoma papilliferum (HP) is a benign neoplasm involving anogenital mammary-like glands and occurs most commonly in the vulva or perianal region of adult white women. It is histopathologically similar to intraductal papilloma of the breast. The lesions are usually solitary, well-demarcated papules or nodules covered with normal skin and are generally less than 10 mm in diameter. The prognosis for HP is good. When these tumors are not located in the anogenital area, they are termed ectopic HP. We present a case of ectopic hidradenoma that presented as a mass on the right arm of a 65-year-old female. To the best of our knowledge, only a single case of ectopic HP has previously been reported on the arm.