Abstract

Primary adenocarcinoma of the vulva is exceptionally rare, accounting for less than 5% of malignant vulvar tumors, and represents a heterogeneous group of entities including sweat gland carcinomas, Bartholin gland adenocarcinomas, extramammary Paget disease and adenocarcinoma of mammary gland type (AMGT). AMGT is the rarest, with less than 40 cases reported in the literature. These tumors are derived from anogenital mammary-like glands located in the interlabial folds, with subtle histological and ultrastructural differences from breast tissue. We describe a case of AMGT in a 39-year-old female with a long-standing nodule on her left prepuce that became ulcerated and painful. Punch biopsy demonstrated a deeply infiltrative proliferation of atypical epithelial cells with moderate nuclear pleomorphism forming duct-like structures with focal epidermal involvement and lymphovascular invasion. The tumor cells were diffusely positive for CK7, GATA3, ER, PR, AR and negative for SOX10, p63, p40, and GCDFP-15.  EMA and CEAm confirmed ductal differentiation. Based upon an intralesional benign mammary-type gland, limited intraepidermal involvement, lack of diffuse CEA expression, no squamous or mucinous differentiation, and negative mammogram and PET scan, the diagnosis of AMGT was made.  The patient underwent Mohs procedure with negative resection margins. This rare case emphasizes the importance of thorough sampling, IHC, and radiologic correlation when diagnosing and subtyping primary vulvar adenocarcinoma.