Urothelial carcinoma is most commonly located in the bladder and is typically what histologic type?

• A. Transitional cell carcinoma
• B. Adenocarcinoma
• C. Clear cell carcinoma
• D. Squamous cell carcinoma

Answer: (A)

Urothelial tumors arise from the lining of the urinary tract, the urothelium, which is a specialized transitional epithelium that changes shape as the bladder fills and empties. When these cells become cancerous, the classic histology reflects their origin: transitional cell carcinoma. In the bladder, most urothelial tumors are transitional cell carcinomas, and the term urothelial carcinoma is used today to describe this same lineage. The key idea is that the cancer comes from the urothelium, so its histology is transitional cell in nature.

Other histologies—adenocarcinoma (gland-forming), squamous cell carcinoma (from squamous differentiation often due to irritation), and clear cell carcinoma (rare in the bladder)—do not reflect the normal lining of the bladder and therefore are not the typical histologic type for most bladder-based urothelial cancers.