Ectopic Lactating Adenoma of Breast Presenting as a Vulvar Tumor

Ectopic breast tissue is a rare occurrence that has been well-documented along the length of the milk lines. For the most part, ectopic breast is easily recognizable on routine histology; however, difficulties may arise when dealing with tumors arising from such tissues, such as adenomas or carcinomas. We report the case of a 29-year-old pregnant woman who presented with a 1.6-cm cystic lesion in her vulva. Surgical excision was performed which showed a well-circumscribed tumor composed of compact tubular structures lined by columnar cells with round nuclei and small nucleoli devoid of mitotic activity. The tubular structures were remarkable for the presence of numerous clear vacuoles in the cytoplasm resulting in a histologic picture that is indistinguishable from so-called "lactating" adenomas of the breast. Immunohistochemical stains demonstrated nuclear positivity of the cells lining the ductules for estrogen and progesterone receptors, GATA3, and cytoplasmic staining for mammaglobin, supporting the breast origin of the tissue. Recognition of this lesion is of importance to avoid misdiagnosis of malignancy.