Expression of the breast differentiation antigen NY-BR-1 in a phyllodes tumor of the vulva.

We describe a phyllodes tumor of borderline malignancy in the labium majus of a 49-year-old woman. The histogenetic origin of phyllodes tumors in the vulva is controversial. Strong immunoreactivity for NY-BR-1, a novel breast differentiation antigen, was demonstrated within the epithelial components of the phyllodes tumor. A similar expression pattern was observed in mammary-like glands of the vulva. These findings provide further evidence that phyllodes tumors of the vulva might derive from mammary-like glands in the labium majus or from ectopic breast tissue.