Perianal fibroadenoma, case report.

Extramammary fibroadenomas, occurring in the anogenital region, are rare lesions thought to be arising from "mammary-like anogenital sweet glands" described by van der Putte. We present a 42-year-old woman with a slow-growing, 4-cm, well-circumscribed but nonencapsulated mass in perianal region. The cut surface of the lesion was bulging, gray-white, and slightly lobulated. Microscopically, it was identical to mammary fibroadenoma and composed of concurrent glandular and stromal elements. Low columnar or cuboidal cells with focal, apical cytoplasmic snouts lined the glands, whereas the underlying layer had myoepithelial cell features, expressing smooth muscle actin and S-100. Epithelial component was immunoreactive for human milk fat globulin I. Progesterone receptor positivity was 80%, whereas the estrogen receptor expression was 60%. Gross cystic disease fluid protein and human milk fat globulin II were negative. The case is presented to increase the awareness on mammary-like glands of anogenital region, which may give rise to not only fibroadenomas but also fibrocystic disease, phyllodes tumor, carcinoma in situ, invasive carcinoma and lactating adenoma, hidrocystoma, hidradenoma papilliferum, intraductal papilloma, and sclerosing adenosis, although very rare.