Small cell carcinoma arising in a defunctionalized bladder after urinary diversion for a benign condition: A case report and literature review.

Bladder cancer arising in a defunctionalized bladder after urinary diversion is rare. We report a 42-year-old man who developed pure small cell carcinoma 20 years after diversion for childhood trauma. Lower abdominal discomfort and increasing intravesical fluid accumulation prompted reevaluation. Preoperative biopsy was interpreted as urothelial carcinoma, whereas the cystectomy specimen revealed pure small cell carcinoma. He underwent radical cystectomy followed by adjuvant etoposide and cisplatin chemotherapy and remained recurrence-free for 15 years. This case highlights the importance of long-term follow-up, reassessment of new or worsening clinical findings, and recognition of potential sampling limitations of a small biopsy specimen.