A Papillary hidradenoma, also hidradenoma papilliferum, is a sharply circumscribed nodule of ectopic breast tissue usually found on the labia majora or the interlabial folds. It is benign tissue (not cancerous) but is often confused clinically with carcinoma of the vulva because of its tendency to ulcerate. Histologically, it appears identical to an intraductal papilloma of the breast.