True prostatic blue nevus associated with melanosis: case report, histogenesis and review of the literature.

We describe a case of true blue nevus of the prostate associated with prostatic melanosis, occurring in a 66-year-old man, who underwent multiple echo-guided prostatic fine-needle biopsies for a suspect prostatic adenocarcinoma. The histological features observed in the bioptic samples were chronic and acute inflammation, together with the presence of polygonal or elongated dendritic elements, scattered within the fibromuscular stroma and containing in their cytoplasm a brown pigment, staining black with the Fontana Masson stain, negative for the Perls stain, bleaching with potassium permanganate treatment and imunoreactive for S-100 protein. The presence of melanin pigment in the prostate is an extremely rare occurence, which may be due to melanosis, blue nevus and malignant melanoma, the latter showing distinctive cytological atypia. The recognition of each entity is fundamental for clinical and prognostic implications.