Melanosis of the prostate: an immunohistochemical study

We report here a case of prostatic melanosis examined immunohistochemically. The patient was a 70-year-old man with prostatic hyperplasia. Six foci with brown pigmentation were found, not only in stromal cells but also in glandular epithelial cells among many pieces of prostatic tissue. Immunohistochemically, only pigment-laden stromal cells were obviously positive with antibodies to S-100 protein and melanoma (HMB45), but not for CD57, while epithelial cells were only positive for CD57 after depigmentation with bleaching. This is the first report demonstrating immunopositivity of stromal cells for antimelanoma antibody (HMB45), which can label reactive or dysplastic but not normal melanocytes. These results clearly demonstrated that pigment-laden stromal cells are neuroectodermal in origin, and probably reactive or dysplastic but not normal melanocytes.