Abstract

Anogenital mammary-like glands were once believed to be ectopic breast tissue in the milk line, but are now recognized as normal anogenital structures. Lesions affecting these glands bear a remarkable resemblance to their mammary gland counterparts.

We present a rare case of invasive mammary-type ductal carcinoma of the anogenital mammary-like glands in the vulva. A 69-year female without significant past history presented with a 1 cm vulva nodule. Histology shows invasive ductal carcinoma arising from background of encapsulated papillary carcinoma (EPC) and focal ductal carcinoma in situ (DCIS). Tumor cells are strongly positive for GATA3, ER(100%), and PR(70%).  Immunostains for CK5/6 and p40 highlight myoepithelial cells surrounding small foci of DCIS. No myoepithelial cells are seen along the papillae and around the periphery of encapsulated papillary carcinoma or invasive component.

EPC is a rare malignant breast tumor that is characterized by a low-grade papillary growth of luminal epithelial cells accompanied by thin fibrovascular cores. Histologically, this tumor closely mimics hidradenoma papilliferum and intraductal papilloma of the breast. However, the absence of a myoepithelial layer supports the diagnosis of carcinoma.

"Hidradenocarcinoma papilliferum" is an extremely rare malignant counterpart of hidradenoma papilliferum. There are only a few reports of DCIS or infiltrating carcinoma arising within a preexisting benign hidradenoma papilliferum.

Tumors of anogenital mammary-like glands show a closer resemblance to primary lesions of the breast than of skin. Therefore, it is advisable to compare lesions of these structures to similar, well-established lesions that occur in the breast, rather than cutaneous adnexal tumors.