Advanced vulvar adenocarcinoma of mammary gland type: a case report.

Vulvar adenocarcinoma of mammary gland type (AMGT) is a rare, locally aggressive neoplasm of anogenital mammary-like glands that mimics the histologic and immunophenotypic features of breast carcinoma. Fewer than 60 cases have been described in the literature since the first documented case in 1936. The extreme rarity and resemblance to breast carcinoma complicate diagnosis and treatment. This report presents a case of AMGT in a 61-year-old woman who presented with a palpable, subcutaneous lesion of the lateral mons pubis and labia minora. Initial biopsy identified the lesion as metastatic carcinoma, but immunohistochemical (IHC) analysis and PET/CT indicated a vulvar adenocarcinoma with local nodal metastasis. Aggressive management with radical vulvectomy and bilateral inguinofemoral lymphadenectomy with thorough specimen evaluation by surgical pathology led to the final diagnosis of AMGT TNM stage pT1bpN2cM0 and vulvar FIGO Stage IIIC. IHC staining identified the tumor as ER, PR, and 3+ HER2 positive. Breast cancer treatment guidelines informed the ultimate systemic therapy regimen of docetaxel, carboplatin, trastuzumab, and pertuzumab. Maintenance therapy with trastuzumab and anastrozole was utilized. The patient remained in remission from AMGT 24 months following completion of chemotherapy. While the diagnosis of AMGT poses a unique challenge, IHC staining and imaging to rule out metastatic carcinoma can support the ultimate diagnosis. The sustained remission in this case supports the extrapolation of treatment from vulvar and breast cancer guidelines. Additionally, this case suggests the utility of hormone receptor- and HER2-targeted therapies for systemic treatment.