Ultrasound of the prostate demonstrates a large irregular prostate, bulging into the base of the bladder, which itself appears thick walled, suggesting hypertrophy. 

CT, performed only with oral contrast (due to renal impairment) confirms the abnormality. The prostatic mass has ill-defined margins with evidence of invasion into the seminal vesicles. Numerous enlarged pelvic nodes are present and both kidneys are hydronephrotic. 

The lungs contain innumerable pulmonary metastases. 

The appearances are those of a malignant prostatic mass (stage IV). The differential includes advanced prostate cancer, TCC of the bladder base, SCC of the urethra, sarcoma, primary melanoma of the prostate. 

Histology

Microscopic description: The sections show cores of prostatic parenchyma infiltrated by a malignant epithelioid and spindled tumor showing abundant cytoplasmic melanin pigment, indicating a diagnosis of melanoma.   Foci of tumor necrosis are present.

Immunohistochemical stains have been performed on this tumor. The tumor cells are positive for  S100, HMB-45 and Melan A,  confirming the diagnosis of melanoma.

Final diagnosis: Prostate TRUS biopsies : melanoma