Mammary-like gland adenoma of the vulva: review of 46 cases

Aims: Hidradenoma papilliferum (HP) of the anogenital region, which was previously thought to be an apocrine tumour, is now believed to be derived from anogenital mammary-like glands (MLG) and is more accurately termed MLG adenoma. We sought to explore any ramifications that may have resulted from the perceived change in histogenesis of this tumour. Methods: We performed a clinicopathological audit of 46 cases. Results: The mean age was 52 years and the range 31-90 years. Symptoms occurred in 23%, comprising nodules of increasing size 9%, pruritus 9% and bleeding 6%. Tumours occurred in the known distribution of mammary-like glands. The labia minora accounted for 50%, labia majora 40%, fourchette 7% and clitoris 3%. Tumours were described clinically as cystic in 42%, ulcerated 33% and solid 25%. Histologically, adjacent normal MLG were often present. There was striking diversity in histology. Tubular, papillary, cystic and solid areas were seen in various combinations. Two cell types, epithelial and myoepithelial, were present. The most common epithelial cell, the ductal cell, was seen alone in 43% or associated with apocrine metaplasia (57%) and/or foam cells (13%) and/or squamous cells (13%). Myoepithelial cells were usually flattened, but were prominent and clear cell in type in 11%. Stroma was variable in amount and either desmoplastic or sclerotic. Inflammatory cells were particularly associated with tumours involving the surface. Unusual architectural patterns resembled breast lesions such as erosive adenomatosis, sclerosing adenosis and ductal adenoma. No recurrence or association with malignancy was recorded. Conclusions: MLG adenomas demonstrate a marked diversity in histological pattern and cell morphology. The ductal cell and a site compatible with and/or the presence of adjacent normal MLG are the most characteristic features. Unusual vulvar tumours, which have been previously reported as erosive adenomatosis, sclerosing adenosis, papillary adenofibroma, syringocystadenoma papilliferans, etc., are variants of MLG adenomas.