The 2004 World Health Organization/International Society of Urological Pathology classification system for non-muscle-invasive bladder cancer

Urothelial carcinoma is the most common neoplasm of the bladder. More than half of all bladder urothelial carcinomas present as papillary, non-muscle-invasive bladder cancers (NMIBCs), being either noninvasive (Ta) or lamina propria invasive (T1). The rest are high-grade and muscularis propria invasive. Because these two tumor groups behave differently in recurrence, progression, and cancer-related mortality, different treatment strategies are applied. NMIBCs are usually treated by transurethral resection (TUR) followed by intravesical instillation, whereas high-grade, muscleinvasive tumors are eligible for cystectomy. Due to the unfavorable prognosis of muscle-invasive tumors, prognostic indicators that are able to predict a subset of NMIBC likely to progress are needed to tailor more aggressive surveillance and management.