Ectopic hidradenoma papilliferum: a case report and review of the literature.

Hidradenoma papilliferum is a benign, cystic, papillary tumor that occurs almost exclusively in women on the skin of the anogenital region. Nonanogenital (ectopic) hidradenoma papilliferum are rare. We describe a 72-year-old white man with an enlarging nodule in the region of the right triceps muscle; microscopic examination showed a hidradenoma papilliferum. The median age of patients with ectopic hidradenoma papilliferum is between 1 to 2 decades older than the average age range of lesion onset in patients with anogenital hidradenoma papilliferum. In contrast to anogenital hidradenoma papilliferum, nearly one half of the patients with ectopic hidradenoma papilliferum are men. Ectopic hidradenoma papilliferum occurs most frequently (60%) in the head and neck region. Eighty-five percent of cases are 1.5 cm in the greatest diameter or smaller. The race, clinical features, pathologic features, treatment, and prognosis for hidradenoma papilliferum occurring in anogenital and ectopic locations are similar.