Nonmuscle invasive urothelial cancer— Bacillus Calmette–Guérin instillation or checkpoint inhibitor immunotherapy?

Summary To date, intravesical instillation of Bacillus Calmette–Guérin (BCG) is the standard adjuvant treatment for most intermediate- and all high-risk bladder nonmuscle invasive urothelial carcinomas (NMIBC) after complete transurethral resection. Although BCG immunotherapy successfully reduces both recurrence and progression rates in affected patients, there are certain limitations associated with its application. Major issues are the relatively high failure rate in up to 40% of patients, the adverse effects of the instillations, and the shortage in BCG supply, requiring concerted alternative strategies. Furthermore, radical cystectomy, the currently suggested salvage treatment for patients failing BCG therapy, is often an overtreatment for a significant proportion of patients. Checkpoint inhibitor (CKI) immunotherapy has proven to be highly effective in a subset of advanced bladder cancer patients and is currently tested in various clinical scenarios alone and in combination with BCG in the adjuvant setting. CKIs’ mechanism is to a large part similar to that reported for BCG—that is, activation of the immune system and elimination of cancer cells in the bladder. Furthermore, CKIs could synergistically enhance the effect of the immune system attracted by BCG and are generally associated with acceptable rates of adverse reactions. Thus, they may represent an ideal alternative to or partner for BCG immunotherapy in NMIBC. In case the recent encouraging results of currently ongoing trials translate into tangible improved outcomes, the combination of CKI and BCG immunotherapy can be expected to represent a valid treatment strategy for well-selected nonmuscle invasive bladder cancer patients in the future.