The high recurrence and progression rates of non-muscle invasive bladder cancer (NMIBC) have led investigators to study the use of intravesical therapy in order to prevent them. Bacillus Calmette–Guérin (BCG) has been successfully used for this indication to treat NMIBC for more than four decades.

BCG is the only intravesical agent shown to reduce the risk of progression of NMIBC to muscle-invasive disease. Despite over 40 years of clinical use, the precise mechanism of action for what has often been considered the most successful cancer immunotherapy in humans remains largely unknown.

Unfortunately, BCG therapy is not a universal panacea and it still fails in up to 40% of patients. Many of these patients, especially in the high-risk category (T1 high-grade disease, carcinoma in situ) will require aggressive therapy like cystectomy or in selected cases, bladder-sparing options like chemo-radiation. Indeed, there is no gold standard intravesical treatment after BCG failure.