Under the Microscope: How would you diagnose this case?

A 39-year-old woman with external hemorrhoids underwent a hemorrhoidectomy. Grossly, the specimen was described as an ellipse of dark brown skin and underlying soft tissue, which on sectioning contained a tan, fleshy nodule (0.9 cm). Photomicrographs of the nodule are shown below (Figures 1 and 2).

What is your diagnosis?
a) Fibrotic hemorrhoid. d) Fibroadenoma of the anogenital region.
b) Well-differentiated anal gland adenocarcinoma. e) Leiomyoma.
c) Endometriosis.

Answer: D. Fibroadenoma of the anogenital region.

Histologic sections show a well-circumscribed nodule that is sharply demarcated from the overlying skin. The lesion consists of both glandular and stromal elements. The stroma is fibrotic and hypocellular with no atypia. The epithelium lining the glandular component is cuboidal to columnar with apical snouts and is cytologically benign. The epithelium is variably positive for estrogen (figure 3) and progesterone receptors by immunohistochemistry, supporting the diagnosis of fibroadenoma.

Fibroadenomas are the most common benign tumors of the breast, and they rarely occur in extramammary sites. In the anogenital region, they are believed to arise from mammary-like sweat glands of the skin. These are most likely eccrinetype glands that undergo at least partial transformation to an apocrine phenotype, thereby gaining the ability to from breast structures. It is important for pathologists to be aware of this phenomenon, as these transformed anogenital glands may not only give rise to benign breast lesions, but also to malignant tumors, including extramammary Paget disease and invasive adenocarcinoma. The lesion presented here, however, is clearly benign as evidenced by its bland histomorphologic features. Also, by immunohistochemistry (not shown), an intact myoepithelial layer and very low proliferative rate provided additional confirmation of the benign nature of this lesion. l

Solomon GJ et al. A 65-year-old woman with a “hemorrhoid.” Fibroadenoma of
the anogenital region. Arch Path Lab Med 2006;130:e30-32.

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