Microscopic description and IHC:

Sections show a circumscribed lesion composed of papillary structures/glands that are lined by two layers of cells. On immunostains, the inner columnar cells are positive for CK7 and ER. The outer myoepithelial are positive for p63.

Discussion:

Hidradenoma Papilliferum (HP), also known as papillary hidradenoma, is a benign cystic neoplasm that usually occurs as a solitary lesion <2cm in the anogenital area of middle-aged women. It can occur outside the anogenital area and would then be considered “ectopic.”

HP is derived from anogenital mammary-like glands. These lesions are histopathologically very similar to those seen in the breast.

Hidradenoma papilliferum is usually a benign lesion with a good prognosis.

Malignant transformation, while rare, can occur, thus excision is recommended.

References:

Konstantinova, Anastasia M., et al. “Hidradenoma Papilliferum.” The American Journal of Dermatopathology, vol. 38, no. 8, 2016, pp. 598–607.

Huddleston M, Jenkins C, Nelson E. Hidradenoma Papilliferum: A Case Report of an Uncommon Perianal Lesion. The American Surgeon [serial online]. February 2016;82(2):E43-E44. 

CASE IMAGES