Pigmented lesions in the prostate are rare and include blue nevus and melanosis. In the prostate, the term "blue nevus" has been used when melanin is confined to the melanocytes in the stroma and the term “melanosis" has been variably applied for a grossly apparent lesion and/or microscopically conspicuous melanin pigment found both in the glandular epithelium and within histiocytes in the stroma.
There have been about 30 reported cases of prostatic blue nevus and/or melanosis since the report by Nigogosyan et al. of the first case of a pigmented lesion in the prostate in 1963. About two-thirds of the pigmented lesions are blue nevi and one-third melanosis. The histogenesis of melanin-containing lesions in the prostate is unknown. Most investigators believe that melanin is produced by migrating melanocytes in the stroma, which is then transferred to the glandular epithelium.
The age of recorded patients with blue nevus or melanosis ranged from 20 to 80 years (mean 68 years) and the finding was usually incidental, the most common clinical presentation being urinary tract obstruction; the usual clinical diagnosis was BPH. Occasionally, malignant melanoma was suspected intraoperatively because of diffuse dark staining of the prostate. Black to brown discoloration was visible in some lesions on gross examination. Microscopically, pigmented spindle cells with long dendritic processes are found scattered in the stroma, close to the prostatic acini. The cytoplasm of the spindle cells contains finely granular, brown or black pigment. The pigment is positive for Fontana-Masson and Lillies ferrous iron stains for melanin. On ultrastructural analysis, the spindle cells, contain different stages of melanosomes in white men and only mature type IV melanosomes in black men.
Although Das Gupta et al. have stated that no satisfactory instance of primary malignant melanoma of the prostate has been reported, a possible case was described by Berry & Reese.
More recently, attention has been focused on pigment that is frequently noted in prostatic epithelium upon closer scrutiny. This pigment, characterized as lipofuscin by virtue of its positivity for Fontana-Masson, Ziehl-Neelsen stain, Luxol fast blue and oil red 0, is present in 10-100% of the prostate glands. The incidence, of pigment was greater if the entire gland was examined, or if special stains were used for detection. This lipofuscin pigment is present in all zones of the prostate, in normal prostate and in several pathologic condition including high-grade PIN and cancer. The pigment is usually fine, golden-yellow, intranuclear or occurring, throughout the cytoplasm; when it is conspicuous it may appear to be golden-brown or blue. It is more fine and less refractile than seminal vesicle lipofuscin pigment. The pigment in the prostate is thought to represent “wear and tear" and "aging pigment" due to accumulation of endogenous by-products within the cell. Awareness of this pigment in prostate is critical, particularly in scant biopsies. Glands with nuclear atypia and pigment should not be automatically interpreted as seminal vesicle/ejaculatory duct epithelium and the possibility of PIN or cancer should be appropriately considered.
