A case of prostatic urothelial carcinoma with aggressive metastasis: Magnetic resonance imaging as an initial diagnostic clue.

Primary urothelial carcinoma of the prostate is a rare malignancy that is often under-recognized because of its nonspecific clinical presentation and imaging features. Herein, we report a case of a 76-year-old man who was incidentally found to have multiple pulmonary and hepatic nodules and pelvic lymphadenopathy during preoperative imaging for valvuloplasty. These findings raised suspicion of metastatic disease. The primary origin was initially suspected to be bladder or rectal cancer. Gastrointestinal evaluations were unremarkable. Cystoscopy revealed multiple bladder tumors but no abnormalities in the prostatic urethra. Prostate-specific antigen (PSA) levels were within the normal range. Magnetic resonance imaging showed no distinct prostatic mass; however, diffusion-weighted imaging revealed diffuse diffusion restriction in the prostate, suggestive of malignancy. The patient underwent simultaneous transurethral resection of the bladder tumor and transperineal prostate biopsy. Both specimens revealed high-grade urothelial carcinoma. Immunohistochemical staining was positive for cytokeratin (CK) 7, CK20, and GATA3, and negative for PSA, consistent with urothelial origin. The tumor showed more extensive and aggressive involvement in the prostate than in the bladder, suggesting that the prostate was the primary site. This case highlights the importance of careful prostate evaluation when assessing urothelial carcinoma, particularly in cases with normal PSA levels and without bladder wall invasion. As the prostate is a potential primary site of urothelial carcinoma, clinical awareness of this rare malignancy is necessary.